Placing firework-rocket-monsterspawners crashes the game.

way to reproduce:
1: do "/give (your username) 52 1 22"
2: place the monsterspawner.
1: try placing a firework rocket spawner with MCedit
2: open your world in minecraft.
3: experience a fun-spoiling crash.

i know its not a very important bug, but it would be fun if it worked!