Windows 7 x64
I have the project and maven projects tool window placed on the top left side together. They don't have docked or floating mode enabled so it behaves like autohide when I focus back into the editor. What is happening consistently is if I switch between tool windows that are grouped together and that autohide, the tool window opens up and retracts back into its home panel when I select it. It shouldn't autohide or collapse back into its original spot unless I focus to the editor.
To recreate this, put project, maven projects tool windows on the top left side together. This might be recreatable with any set of tool windows. Uncheck docked and float mode. Click on Project tool window and let the window display normally, now click on the Maven Projects tool window. The Project window should collapse back and the Maven Project window should now display. Just click back and forth between Projects and Maven Projects repeatedly and you will notice one of the windows will expand and shrink back immediately without user intervention.