Bug with 1.8.8 and 1.9 snapshots playing downloaded maps.

When I play a downloaded world on 1.8.8 or a 1.9 snapshot sometimes it doesn't load and I just hang in the air, and when I try to quit the game it doesn't work.

What I expected to happen was just to play the map I guess and for it to load. And when I try to quit the game for it to just quit normally.

The map doesn't load and I hang in the air. When I try to quit the map it freezes minecraft and I have to force quit the game

I'm not sure what I should right about how to trigger the bug.