I made four enclosures (11 by 11 fences) which shared a middle fence since the enclosures were right next to each other. I put Sheep, Cows, Pigs, and Chickens in separate enclosures, one for each type of animal. After a few Minecraft days I noticed that some of the animals have managed to get into each other's enclosures. These enclosures are one fence tall and COMPLETELY made of fences. One Sheep and one Pig even made it completely out of any enclosure. This is a very annoying bug and I hope it will be resolved soon.