Sorry, if this bug is a duplication. I didn't find this bug on JIRA yet.
This bug affects the Minecraft Singleplayer and Multiplayer.
When I catch some mobs (cows, chickens, sheeps etc.) in fences, they should stay in that compound. They do so... Until I save my world and reload it / until I restart my server.
Then some mobs glitched out the fences and stay in my house or go far away, never to be seen again
I believe, that some mobs are "in the fence-block", when I save the world and Minecraft thinks they are outside the compound and saves them outside of it.
I hope that bug gets fixed, because my mobs are going anywhere after each world save, right now