Hostile Mobs not spawning in v0.12.1 alpha

After the upgrade to v.0.12.1 alpha, I am no longer able to spawn hostile mobs. Here's a list of eggs that won't spawn:
Creeper, Endermen, Silverfish, Skeleton, Slime, Spider, Zombie, Zombie Pigman, Cave Spider, Magma cube, Ghast, Blaze

I am able to spawn these eggs: Villager, Chicken, Cow, Pig, Sheep, Wolf, Ocelot, Mushroom, Bat, Squid

I have tried both in creative and survival.