baby mobs (cows, pigs) will go trough blocks wenn they are in one by one holes(solid blocks)

Put the summary of the bug you're having here

What I expected to happen was...:
i expected that the baby(cows/pigs) would stay in the one by one hole

What actually happened was...:
they did go trough the blocks
Steps to Reproduce:
1. use mob eggs to spawn them in a one by one hole
2. log out
3. log in
4. they will be out of the one by one hole