Passive Mobs Spawning on Roofs and in houses

I have well-lit roofs so hostile mobs don't spawn, but this doesn't stop animals such as Horses, Donkeys, Cows, Pigs, Sheep and Chickens from spawning on the roofs. They are not made of grass blocks, which I thought was a requirement for Passive Animals to spawn. This is really frustrating because they make a lot of unwanted noise and are a pain to kill sometimes. They also spawn inside the houses sometimes which can just get annoying having to repeatedly kill them every time you come back to the house. Very annoying bug, please fix.