I have a Visual Studio project which always appears in the build output even when nothing has changed within it. Nothing actually appears to be being compiled within it though for example, if everything else in a project using this project is built, I would see something like this:
1>------ Build started: Project: MyLib, Configuration: Release Win32 ------
1> MyLib.vcxproj -> C:\Projects\MySoftware\Release\MyLib.dll
========== Build: 1 succeeded, 0 failed, 23 up-to-date, 0 skipped ==========
Turned out the offending project was referencing a header file that didn't exist but wasn't actually included from anywhere so didn't throw up an error. Removing that file from the project solved the issue.