animals keep walking through cobblestone walls

Put the summary of the bug you're having here:
Sheep, pigs, cows, chicken, and their baby's keep walking through cobblestone walls.
I have 6 pigs in a 6x6 wall and they just keep walking out

Steps to Reproduce:
1. create, for example 4x4 cobblestone wall
2. put any animal in it, cows, sheep, pigs, chicken
3. watch them push their way out.