Why "Failed to define class" WARN from server startup?

When I execute liquibase in JBoss I get the following WARN but everything is updated correctly:
12:32:01,499 WARN  [org.jboss.modules] (ServerService Thread Pool -- 49) Failed to define class liquibase.sdk.watch.WatchCommand$DynamicContentHandler in Module "deployment.WebStories.war:main" from Service Module Loader: java.lang.LinkageError: Failed to link liquibase/sdk/watch/WatchCommand$DynamicContentHandler (Module "deployment.WebStories.war:main" from Service Module Loader)
    at org.jboss.modules.ModuleClassLoader.defineClass(ModuleClassLoader.java:407) [jboss-modules.jar:1.2.0.CR1]
    at org.jboss.modules.ModuleClassLoader.loadClassLocal(ModuleClassLoader.java:254) [jboss-modules.jar:1.2.0.CR1]
    at org.jboss.modules.ModuleClassLoader$1.loadClassLocal(ModuleClassLoader.java:73) [jboss-modules.jar:1.2.0.CR1]
    at org.jboss.modules.Module.loadModuleClass(Module.java:518) [jboss-modules.jar:1.2.0.CR1]
    at org.jboss.modules.ModuleClassLoader.findClass(ModuleClassLoader.java:182) [jboss-modules.jar:1.2.0.CR1]
    at org.jboss.modules.ConcurrentClassLoader.performLoadClassUnchecked(ConcurrentClassLoader.java:468) [jboss-modules.jar:1.2.0.CR1]
    at org.jboss.modules.ConcurrentClassLoader.performLoadClassChecked(ConcurrentClassLoader.java:456) [jboss-modules.jar:1.2.0.CR1]
    at org.jboss.modules.ConcurrentClassLoader.performLoadClass(ConcurrentClassLoader.java:398) [jboss-modules.jar:1.2.0.CR1]
    at org.jboss.modules.ConcurrentClassLoader.loadClass(ConcurrentClassLoader.java:120) [jboss-modules.jar:1.2.0.CR1]
    at liquibase.servicelocator.DefaultPackageScanClassResolver.loadClass(DefaultPackageScanClassResolver.java:358) [liquibase-core-3.2.2.jar:]
    at liquibase.servicelocator.DefaultPackageScanClassResolver.loadImplementationsInJar(DefaultPackageScanClassResolver.java:406) [liquibase-core-3.2.2.jar:]
    at liquibase.servicelocator.DefaultPackageScanClassResolver.findAllClasses(DefaultPackageScanClassResolver.java:226) [liquibase-core-3.2.2.jar:]
    at liquibase.servicelocator.DefaultPackageScanClassResolver.find(DefaultPackageScanClassResolver.java:116) [liquibase-core-3.2.2.jar:]
    at liquibase.servicelocator.DefaultPackageScanClassResolver.findImplementations(DefaultPackageScanClassResolver.java:84) [liquibase-core-3.2.2.jar:]
    at liquibase.servicelocator.ServiceLocator.findClassesImpl(ServiceLocator.java:202) [liquibase-core-3.2.2.jar:]
    at liquibase.servicelocator.ServiceLocator.findClasses(ServiceLocator.java:177) [liquibase-core-3.2.2.jar:]
    at liquibase.database.DatabaseFactory.<init>(DatabaseFactory.java:25) [liquibase-core-3.2.2.jar:]
    at liquibase.database.DatabaseFactory.getInstance(DatabaseFactory.java:40) [liquibase-core-3.2.2.jar:]
    at liquibase.integration.servlet.LiquibaseServletListener.executeUpdate(LiquibaseServletListener.java:211) [liquibase-core-3.2.2.jar:]
    at liquibase.integration.servlet.LiquibaseServletListener.contextInitialized(LiquibaseServletListener.java:106) [liquibase-core-3.2.2.jar:]
    at org.apache.catalina.core.StandardContext.contextListenerStart(StandardContext.java:3339) [jbossweb-7.2.0.Final.jar:7.2.0.Final]
    at org.apache.catalina.core.StandardContext.start(StandardContext.java:3777) [jbossweb-7.2.0.Final.jar:7.2.0.Final]
    at org.jboss.as.web.deployment.WebDeploymentService.doStart(WebDeploymentService.java:156) [jboss-as-web-7.2.0.Alpha1-redhat-4.jar:7.2.0.Alpha1-redhat-4]
    at org.jboss.as.web.deployment.WebDeploymentService.access$000(WebDeploymentService.java:60) [jboss-as-web-7.2.0.Alpha1-redhat-4.jar:7.2.0.Alpha1-redhat-4]
    at org.jboss.as.web.deployment.WebDeploymentService$1.run(WebDeploymentService.java:93) [jboss-as-web-7.2.0.Alpha1-redhat-4.jar:7.2.0.Alpha1-redhat-4]
    at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471) [rt.jar:1.7.0_11]
    at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:334) [rt.jar:1.7.0_11]
    at java.util.concurrent.FutureTask.run(FutureTask.java:166) [rt.jar:1.7.0_11]
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110) [rt.jar:1.7.0_11]
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603) [rt.jar:1.7.0_11]
    at java.lang.Thread.run(Thread.java:722) [rt.jar:1.7.0_11]
    at org.jboss.threads.JBossThread.run(JBossThread.java:122)
Caused by: java.lang.NoClassDefFoundError: org/eclipse/jetty/server/handler/AbstractHandler
    at java.lang.ClassLoader.defineClass1(Native Method) [rt.jar:1.7.0_11]
    at java.lang.ClassLoader.defineClass(ClassLoader.java:791) [rt.jar:1.7.0_11]
    at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142) [rt.jar:1.7.0_11]
    at org.jboss.modules.ModuleClassLoader.doDefineOrLoadClass(ModuleClassLoader.java:338) [jboss-modules.jar:1.2.0.CR1]
    at org.jboss.modules.ModuleClassLoader.defineClass(ModuleClassLoader.java:402) [jboss-modules.jar:1.2.0.CR1]
    ... 31 more
Caused by: java.lang.ClassNotFoundException: org.eclipse.jetty.server.handler.AbstractHandler from [Module "deployment.WebStories.war:main" from Service Module Loader]
    at org.jboss.modules.ModuleClassLoader.findClass(ModuleClassLoader.java:190) [jboss-modules.jar:1.2.0.CR1]
    at org.jboss.modules.ConcurrentClassLoader.performLoadClassUnchecked(ConcurrentClassLoader.java:468) [jboss-modules.jar:1.2.0.CR1]
    at org.jboss.modules.ConcurrentClassLoader.performLoadClassChecked(ConcurrentClassLoader.java:456) [jboss-modules.jar:1.2.0.CR1]
    at org.jboss.modules.ConcurrentClassLoader.performLoadClass(ConcurrentClassLoader.java:398) [jboss-modules.jar:1.2.0.CR1]
    at org.jboss.modules.ConcurrentClassLoader.loadClass(ConcurrentClassLoader.java:120) [jboss-modules.jar:1.2.0.CR1]
    ... 36 more

12:32:01,532 WARN  [org.jboss.modules] (ServerService Thread Pool -- 49) Failed to define class liquibase.sdk.supplier.database.AllDatabaseTypes in Module "deployment.WebStories.war:main" from Service Module Loader: java.lang.LinkageError: Failed to link liquibase/sdk/supplier/database/AllDatabaseTypes (Module "deployment.WebStories.war:main" from Service Module Loader)
    at org.jboss.modules.ModuleClassLoader.defineClass(ModuleClassLoader.java:407) [jboss-modules.jar:1.2.0.CR1]
    at org.jboss.modules.ModuleClassLoader.loadClassLocal(ModuleClassLoader.java:254) [jboss-modules.jar:1.2.0.CR1]
    at org.jboss.modules.ModuleClassLoader$1.loadClassLocal(ModuleClassLoader.java:73) [jboss-modules.jar:1.2.0.CR1]
    at org.jboss.modules.Module.loadModuleClass(Module.java:518) [jboss-modules.jar:1.2.0.CR1]
    at org.jboss.modules.ModuleClassLoader.findClass(ModuleClassLoader.java:182) [jboss-modules.jar:1.2.0.CR1]
    at org.jboss.modules.ConcurrentClassLoader.performLoadClassUnchecked(ConcurrentClassLoader.java:468) [jboss-modules.jar:1.2.0.CR1]
    at org.jboss.modules.ConcurrentClassLoader.performLoadClassChecked(ConcurrentClassLoader.java:456) [jboss-modules.jar:1.2.0.CR1]
    at org.jboss.modules.ConcurrentClassLoader.performLoadClass(ConcurrentClassLoader.java:398) [jboss-modules.jar:1.2.0.CR1]
    at org.jboss.modules.ConcurrentClassLoader.loadClass(ConcurrentClassLoader.java:120) [jboss-modules.jar:1.2.0.CR1]
    at liquibase.servicelocator.DefaultPackageScanClassResolver.loadClass(DefaultPackageScanClassResolver.java:358) [liquibase-core-3.2.2.jar:]
    at liquibase.servicelocator.DefaultPackageScanClassResolver.loadImplementationsInJar(DefaultPackageScanClassResolver.java:406) [liquibase-core-3.2.2.jar:]
    at liquibase.servicelocator.DefaultPackageScanClassResolver.findAllClasses(DefaultPackageScanClassResolver.java:226) [liquibase-core-3.2.2.jar:]
    at liquibase.servicelocator.DefaultPackageScanClassResolver.find(DefaultPackageScanClassResolver.java:116) [liquibase-core-3.2.2.jar:]
    at liquibase.servicelocator.DefaultPackageScanClassResolver.findImplementations(DefaultPackageScanClassResolver.java:84) [liquibase-core-3.2.2.jar:]
    at liquibase.servicelocator.ServiceLocator.findClassesImpl(ServiceLocator.java:202) [liquibase-core-3.2.2.jar:]
    at liquibase.servicelocator.ServiceLocator.findClasses(ServiceLocator.java:177) [liquibase-core-3.2.2.jar:]
    at liquibase.database.DatabaseFactory.<init>(DatabaseFactory.java:25) [liquibase-core-3.2.2.jar:]
    at liquibase.database.DatabaseFactory.getInstance(DatabaseFactory.java:40) [liquibase-core-3.2.2.jar:]
    at liquibase.integration.servlet.LiquibaseServletListener.executeUpdate(LiquibaseServletListener.java:211) [liquibase-core-3.2.2.jar:]
    at liquibase.integration.servlet.LiquibaseServletListener.contextInitialized(LiquibaseServletListener.java:106) [liquibase-core-3.2.2.jar:]
    at org.apache.catalina.core.StandardContext.contextListenerStart(StandardContext.java:3339) [jbossweb-7.2.0.Final.jar:7.2.0.Final]
    at org.apache.catalina.core.StandardContext.start(StandardContext.java:3777) [jbossweb-7.2.0.Final.jar:7.2.0.Final]
    at org.jboss.as.web.deployment.WebDeploymentService.doStart(WebDeploymentService.java:156) [jboss-as-web-7.2.0.Alpha1-redhat-4.jar:7.2.0.Alpha1-redhat-4]
    at org.jboss.as.web.deployment.WebDeploymentService.access$000(WebDeploymentService.java:60) [jboss-as-web-7.2.0.Alpha1-redhat-4.jar:7.2.0.Alpha1-redhat-4]
    at org.jboss.as.web.deployment.WebDeploymentService$1.run(WebDeploymentService.java:93) [jboss-as-web-7.2.0.Alpha1-redhat-4.jar:7.2.0.Alpha1-redhat-4]
    at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471) [rt.jar:1.7.0_11]
    at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:334) [rt.jar:1.7.0_11]
    at java.util.concurrent.FutureTask.run(FutureTask.java:166) [rt.jar:1.7.0_11]
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110) [rt.jar:1.7.0_11]
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603) [rt.jar:1.7.0_11]
    at java.lang.Thread.run(Thread.java:722) [rt.jar:1.7.0_11]
    at org.jboss.threads.JBossThread.run(JBossThread.java:122)
Caused by: java.lang.NoClassDefFoundError: org/junit/experimental/theories/ParameterSupplier
    at java.lang.ClassLoader.defineClass1(Native Method) [rt.jar:1.7.0_11]
    at java.lang.ClassLoader.defineClass(ClassLoader.java:791) [rt.jar:1.7.0_11]
    at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142) [rt.jar:1.7.0_11]
    at org.jboss.modules.ModuleClassLoader.doDefineOrLoadClass(ModuleClassLoader.java:338) [jboss-modules.jar:1.2.0.CR1]
    at org.jboss.modules.ModuleClassLoader.defineClass(ModuleClassLoader.java:402) [jboss-modules.jar:1.2.0.CR1]
    ... 31 more
Caused by: java.lang.ClassNotFoundException: org.junit.experimental.theories.ParameterSupplier from [Module "deployment.WebStories.war:main" from Service Module Loader]
    at org.jboss.modules.ModuleClassLoader.findClass(ModuleClassLoader.java:190) [jboss-modules.jar:1.2.0.CR1]
    at org.jboss.modules.ConcurrentClassLoader.performLoadClassUnchecked(ConcurrentClassLoader.java:468) [jboss-modules.jar:1.2.0.CR1]
    at org.jboss.modules.ConcurrentClassLoader.performLoadClassChecked(ConcurrentClassLoader.java:456) [jboss-modules.jar:1.2.0.CR1]
    at org.jboss.modules.ConcurrentClassLoader.performLoadClass(ConcurrentClassLoader.java:398) [jboss-modules.jar:1.2.0.CR1]
    at org.jboss.modules.ConcurrentClassLoader.loadClass(ConcurrentClassLoader.java:120) [jboss-modules.jar:1.2.0.CR1]
    ... 36 more

12:32:01,546 WARN  [org.jboss.modules] (ServerService Thread Pool -- 49) Failed to define class liquibase.sdk.supplier.database.AllDatabases in Module "deployment.WebStories.war:main" from Service Module Loader: java.lang.LinkageError: Failed to link liquibase/sdk/supplier/database/AllDatabases (Module "deployment.WebStories.war:main" from Service Module Loader)
    at org.jboss.modules.ModuleClassLoader.defineClass(ModuleClassLoader.java:407) [jboss-modules.jar:1.2.0.CR1]
    at org.jboss.modules.ModuleClassLoader.loadClassLocal(ModuleClassLoader.java:254) [jboss-modules.jar:1.2.0.CR1]
    at org.jboss.modules.ModuleClassLoader$1.loadClassLocal(ModuleClassLoader.java:73) [jboss-modules.jar:1.2.0.CR1]
    at org.jboss.modules.Module.loadModuleClass(Module.java:518) [jboss-modules.jar:1.2.0.CR1]
    at org.jboss.modules.ModuleClassLoader.findClass(ModuleClassLoader.java:182) [jboss-modules.jar:1.2.0.CR1]
    at org.jboss.modules.ConcurrentClassLoader.performLoadClassUnchecked(ConcurrentClassLoader.java:468) [jboss-modules.jar:1.2.0.CR1]
    at org.jboss.modules.ConcurrentClassLoader.performLoadClassChecked(ConcurrentClassLoader.java:456) [jboss-modules.jar:1.2.0.CR1]
    at org.jboss.modules.ConcurrentClassLoader.performLoadClass(ConcurrentClassLoader.java:398) [jboss-modules.jar:1.2.0.CR1]
    at org.jboss.modules.ConcurrentClassLoader.loadClass(ConcurrentClassLoader.java:120) [jboss-modules.jar:1.2.0.CR1]
    at liquibase.servicelocator.DefaultPackageScanClassResolver.loadClass(DefaultPackageScanClassResolver.java:358) [liquibase-core-3.2.2.jar:]
    at liquibase.servicelocator.DefaultPackageScanClassResolver.loadImplementationsInJar(DefaultPackageScanClassResolver.java:406) [liquibase-core-3.2.2.jar:]
    at liquibase.servicelocator.DefaultPackageScanClassResolver.findAllClasses(DefaultPackageScanClassResolver.java:226) [liquibase-core-3.2.2.jar:]
    at liquibase.servicelocator.DefaultPackageScanClassResolver.find(DefaultPackageScanClassResolver.java:116) [liquibase-core-3.2.2.jar:]
    at liquibase.servicelocator.DefaultPackageScanClassResolver.findImplementations(DefaultPackageScanClassResolver.java:84) [liquibase-core-3.2.2.jar:]
    at liquibase.servicelocator.ServiceLocator.findClassesImpl(ServiceLocator.java:202) [liquibase-core-3.2.2.jar:]
    at liquibase.servicelocator.ServiceLocator.findClasses(ServiceLocator.java:177) [liquibase-core-3.2.2.jar:]
    at liquibase.database.DatabaseFactory.<init>(DatabaseFactory.java:25) [liquibase-core-3.2.2.jar:]
    at liquibase.database.DatabaseFactory.getInstance(DatabaseFactory.java:40) [liquibase-core-3.2.2.jar:]
    at liquibase.integration.servlet.LiquibaseServletListener.executeUpdate(LiquibaseServletListener.java:211) [liquibase-core-3.2.2.jar:]
    at liquibase.integration.servlet.LiquibaseServletListener.contextInitialized(LiquibaseServletListener.java:106) [liquibase-core-3.2.2.jar:]
    at org.apache.catalina.core.StandardContext.contextListenerStart(StandardContext.java:3339) [jbossweb-7.2.0.Final.jar:7.2.0.Final]
    at org.apache.catalina.core.StandardContext.start(StandardContext.java:3777) [jbossweb-7.2.0.Final.jar:7.2.0.Final]
    at org.jboss.as.web.deployment.WebDeploymentService.doStart(WebDeploymentService.java:156) [jboss-as-web-7.2.0.Alpha1-redhat-4.jar:7.2.0.Alpha1-redhat-4]
    at org.jboss.as.web.deployment.WebDeploymentService.access$000(WebDeploymentService.java:60) [jboss-as-web-7.2.0.Alpha1-redhat-4.jar:7.2.0.Alpha1-redhat-4]
    at org.jboss.as.web.deployment.WebDeploymentService$1.run(WebDeploymentService.java:93) [jboss-as-web-7.2.0.Alpha1-redhat-4.jar:7.2.0.Alpha1-redhat-4]
    at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471) [rt.jar:1.7.0_11]
    at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:334) [rt.jar:1.7.0_11]
    at java.util.concurrent.FutureTask.run(FutureTask.java:166) [rt.jar:1.7.0_11]
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110) [rt.jar:1.7.0_11]
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603) [rt.jar:1.7.0_11]
    at java.lang.Thread.run(Thread.java:722) [rt.jar:1.7.0_11]
    at org.jboss.threads.JBossThread.run(JBossThread.java:122)
Caused by: java.lang.NoClassDefFoundError: org/junit/experimental/theories/ParameterSupplier
    at java.lang.ClassLoader.defineClass1(Native Method) [rt.jar:1.7.0_11]
    at java.lang.ClassLoader.defineClass(ClassLoader.java:791) [rt.jar:1.7.0_11]
    at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142) [rt.jar:1.7.0_11]
    at org.jboss.modules.ModuleClassLoader.doDefineOrLoadClass(ModuleClassLoader.java:338) [jboss-modules.jar:1.2.0.CR1]
    at org.jboss.modules.ModuleClassLoader.defineClass(ModuleClassLoader.java:402) [jboss-modules.jar:1.2.0.CR1]
    ... 31 more
Caused by: java.lang.ClassNotFoundException: org.junit.experimental.theories.ParameterSupplier from [Module "deployment.WebStories.war:main" from Service Module Loader]
    at org.jboss.modules.ModuleClassLoader.findClass(ModuleClassLoader.java:190) [jboss-modules.jar:1.2.0.CR1]
    at org.jboss.modules.ConcurrentClassLoader.performLoadClassUnchecked(ConcurrentClassLoader.java:468) [jboss-modules.jar:1.2.0.CR1]
    at org.jboss.modules.ConcurrentClassLoader.performLoadClassChecked(ConcurrentClassLoader.java:456) [jboss-modules.jar:1.2.0.CR1]
    at org.jboss.modules.ConcurrentClassLoader.performLoadClass(ConcurrentClassLoader.java:398) [jboss-modules.jar:1.2.0.CR1]
    at org.jboss.modules.ConcurrentClassLoader.loadClass(ConcurrentClassLoader.java:120) [jboss-modules.jar:1.2.0.CR1]
    ... 36 more

12:32:01,652 ERROR [stderr] (ServerService Thread Pool -- 49) INFO 23/10/14 12:32: liquibase: Successfully acquired change log lock

12:32:02,336 ERROR [stderr] (ServerService Thread Pool -- 49) INFO 23/10/14 12:32: liquibase: Reading from public.databasechangelog

12:32:02,383 ERROR [stderr] (ServerService Thread Pool -- 49) INFO 23/10/14 12:32: liquibase: Successfully released change log lock
Any stacktrace in the server startup is considered an error, despite it is marked as a WARN, INFO or NOTHING.
Why does that happen?
What can I do to remove this stacktrace from the server startup?
Solution
Liquibase internally scans your classpath using your classloader to find classes that may be Liquibase extensions. Part of that scanning is hitting a few classes that are bundled with the liquibase jar but are not part of the normal liquibase update process.
In particular, it is checking code that displays the database and liquibase state that can be helpful in demos and troubleshooting and other code that can be used for testing extensions.
These non-standard use classes reference additional dependencies such as jetty and junit and which are normally not available in production environments and so Liquibase expects some ClassNotFoundExceptions and DEBUG-level logs them, moves on, and updates correctly as you are seeing.
In your case, it appears that the JBoss classloader has an additional feature to log at WARN level any ClassNotFoundExceptions it runs into throwing it up the chain to the point that Liquibase ignores it.
A future release of Liquibase will better split between the "tools" codebase and the "standard" codebase, but for now your options would be:
Include the missing dependencies in your classpath (jetty and junit based in your stacktrace)
Create enough of a stub class named the same as the referenced jetty and junit classes in order to make the class loader happy.
Set the log level for "org.jboss.modules" to ERROR in order to not log WARN-level logs