Makeing mob spawners with mcedit causes the game to crash

Put the summary of the bug you're having here

What I expected to happen was...:
The spawner to be created and it to spawn mobs as normal

What actually happened was...:
When I entered the world the game crashed

Steps to Reproduce:
1. Spawn a mob in game
2. use a third party tool like mcedit to make a spawner
3. enter the world