Regular mobs spawn in witch huts

Witch huts are supposed to have a 7x9x7 area where only witches can spawn. However in 0.15.0 witch huts have no such area.

Steps to reproduce:

1. Create a world with seed -334399639
2. Destroy the hut right at the spawn point and build spawn pads.
3. There is a GIGANTIC cave which opens near the village. Light it up thoroughly or you'll see no mobs spawning in the hut.
4. Observe that regular mobs like creepers and slimes start spawning in the hut.