I'm beginning to believe this bug is caused by the fact that mobs load before the environment as chunks are loading. I can always see animals and fires before the landscape loads. This may allow mobs to wonder out of enclosures in ways otherwise impossible, or else suffocate when land loads.
Matthew Epperson
Confirmed on MCPE V0.15.4 Ipad 2
I'm beginning to believe this bug is caused by the fact that mobs load before the environment as chunks are loading. I can always see animals and fires before the landscape loads. This may allow mobs to wonder out of enclosures in ways otherwise impossible, or else suffocate when land loads.