What I expected- the spawner to spawn a villager riding a firework that will fly in the air and after the fire work detonated will fall down.
What happened- The spawner crashed my game and corrupted my world.
How to reproduce- cage a villager up high then set off a firework underneath it, then use Sethbling's Stacked entities filter in mcedit on the two. Then use the create spawner filter on the stacked entity.
Why I think this is a bug- All other stacked entities iv tried work fine and do not crash nor corrupt the world.