Spawners disappear 1.8 release/snapshots

I was to continue my map for more than 7 hours.
When I suddenly perceived that no more monsters was spawning, all spawners were gone.
When I go on my world with mcedit, the spawners are present, but they are pigs inside.

What I expected to happen was see monsters spawn..:

What actually happened was the monsters did not spawn and spawners disappeared...:

Steps to Reproduce:
1. Create a spawner with a monster in armor in 1.7.4 using MCEDIT.
2. Download and run the 1.8
3. Load the world