When playing on survival mode in MCPE and you attach any animal to a leash and onto a fence/wall, the mob will stay there. Though, if you go out of the chunk that the mob was in and quit the world. The mob will disappear but the fence/wall will still be there. It's also weird because the lead will still appear to be on the wall/fence, but when taken off, it will disappear fully and not even give the player its lead back.