In 1.8 there is a new feature consisting of right-clicking a spawner with a spawn egg to change the mob type. If you right-click it with "minecraft:spawn_egg" the whole game freezes and then crashes. I have put an attachment of the crash report down below VVV
I hope this will be fixed in the future! 😃
UPDATE: I had to crash my game again to take the screenshot, and when I went back to Single Player my world got deleted!!! D:
Duplicate of MC-61895