Entitys bugging out of Cages

I build a cage (2x2) out of Obsidian.
SP:
Then I spawned lots of Cows and Quit the World.
After I loaded the world, some cows went out of the Cage.

MP:
I spawned lots of Cows and disconnected.
After 10 Minutes I logged back on, and some cows went out of the cage.

~NiklasK2001