Trying to break blocks crashes the game.

I tried breaking stone, dirt, and glass, using a enchanted diamond pickaxe and then an enchanted diamond sword. The game crashes just after the first cracks appear.

What I expected to happen was...:
block breaks

What actually happened was...:
game breaks

Steps to Reproduce:
I connected to server. I can walk around, open chests, etc. but when I try to break a block, crash.