Does it happen with all the video output module. try lauching VLC with -V x11 or -V glx (the default is xvideo)
Also, could you start vlc from a terminal with -vvv --color and look at the log when switching back from fullscreen -- vlc leaving fullscreen causes resolution switch https://launchpad.net/bugs/85676 -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
