Pigs Spawning in Leaves of Trees

I started a brand new survival world in Minecraft PE 1.0.0.7. I was exploring above mountains then I saw pigs inside leaves of trees. I thought that it was only a pig sight piercing through the leaves,but it was true that the pig is actually inside the leaves of the tree. I do not know if other mobs has the same occurance as well. This is my first time seeing a pig inside a tree. Please fix this bug. (Device: Sony Xperia E4g Dual)