I have an egg farm with chickens. When I go back into the game, I noticed most of the chickens teleported into nearby chunks. Since they were in groups, I concluded it was a bug to do with chunks. I also noticed once that when a chunk with the chickens loaded, I saw them teleport. This has also happened with some of my sheep. It seems to be mobs that come from before 0.15.0 that don't teleport, but the mobs that came after I downloaded 0.15.0 teleport. My dogs don't teleport. I tamed my dogs before 0.15.0, but I bred my chickens after I got 0.15.0. I have also bred sheep in my sheep farm after I downloaded 0.15.0 and some have teleported to the next chunk.