itjust crashed with minecraft after itryed to get out of my world, i was using 14w20b -a fan terengrel02

Put the summary of the bug you're having here

What I expected to happen was...:
Describe what you thought should happen here

What actually happened was...:
Describe what happened here

Steps to Reproduce:
1.place lava
2.let it flow
3. then try to close world