Under AVL6 / LXDE, if you have the transport window open and push F11 it makes the transport window full screen instead of hiding it.
It works correctly under Wheezy / KDE.
Seems the LXDE WM has allocated F11 for it's own purposes. I don't see how we can override that, the two solutions you have are:
1. configure LXDE to use some other key for fullscreen
2. configure MusE to use another key for opening the transport