animals go to walls

Animals go to walls/fences.

I first had a fence but mysteriously the broke out. so i made a wall of 2 blocks high inside (on attachement it is 3 blocks on outside)

but annimals still broke out.

What i saw today was that a animal was in the wall and i saw the head sticking out (see attachment). a few seconds later the animal was walking free (on wrong side of my wall).

Steps to Reproduce:
1. animal walks in block (fence or any kins of block)
2. you can see head sticking out om the other side
3. animal walks out on the other side of fence/block and did a wallhack