I was playing the latest snapshot and when i got the the end i noticed that the ender dragon didnt spawn but i didnt think much about it. i destroyed the ender crystals then i spawned the dragon using the clay creeper face. after killing the dragon i explored the new ender islands after going back to the overworld and i noticed that the cows and chickens i had fenced in front of my home had vanished.

i have been able to replicate the bug 3 times in the same world by entering the end and spawned the dragon with the creeper face then when i leave the end the mobs have vanished