Starting Minecraft 1.8 or switching to fullscreen most often than not produces an invisible fullscreen window ontop of everything on the desktop and you have to switch to another tty to kill it.
It works approximately every third time you start so there is still a race condition present. Have the same problem on two computers. Also had this with 1.7.10.
Fullscreen worked in an earlier 1.7.x release on this computer.
I think this relates to