As described at the end of this bug report:
MC-33903
and on this reddit thread:
http://www.reddit.com/r/linux_gaming/comments/35nheg
sometimes in fullscreen the character cannot turn all the way around, but only as far as the invisible cursor can go to the edge of the screen. This doesn't happen all the time, and this behavior goes away when you view the Esc menu, or leave fullscreen and return to it.

15w49b video: https://www.youtube.com/watch?v=qQRadVJmb7o