I have a strange behavior in my app when running in jelly bean 4.1.1 , when i start an Activity and press the back button to go back to the First Activity it re-create it by calling onCreate also , what i did also i handle the configuration change with the first activity so it won't recreated on configuration change but thats didnt make anything . !!!! why Activity life cycle in jelly bean have a strange behavior. You can see what i mean , just create a simple Android project and create two activity , navigate from the first one to activity to and press back button and see the logs onCreate on Activity 1 will be called !!!!
There is no guarentee that the OS won't kill your background Activities at any time if it determines that it needs the resources. Just a guess, but onCreate may get called in these cases because the system kills the first Activity before you get back to it.
Edit: http://developer.android.com/guide/components/activities.html#Lifecycle
If an activity is paused or stopped, the system can drop it from memory either by asking it to finish (calling its finish() method), or simply killing its process. When the activity is opened again (after being finished or killed), it must be created all over.