Farm animals glitching into/through fences

What happened: I decide to take a look at my animals pen but some pigs and chickens have got their heads inside the fence. Some of them are even outside the fence. It is not because they are escaping through the player entrance and exit, which is a block above the fence with a ladder on it. They are right next to the fence and if I hit them the knockback knocks them away from the fence.