Basically if you play in a world, any world, and tame an animal, they lose their tamed "status" after you exit the world. This seems to have affected cats, tamed wolves, and tamed foxes so far. I haven't tried on other mobs such as parrots. 

An example of this bug would be my dog in my survival world. I tamed him about 10 minutes ago and exited the game to do something else. I opened the game right now and now I am unable to control it (telling it to sit or stand) and it will attack me if I hit it. It also won't defend me against monsters. It happens to anyone joining my world via Xbox Live multiplayer (not sure about LAN).