So, I went into superflat in each of these updates, and it began snowing. Off in the distance, I see a zombie jumping and spinning. I laugh, and then look over to the nearby village, to see ~7 villagers doing the same thing with a zombie doing it nearby.

What I expected to happen was...:
Zombie walks on snow. Zombie chases villager to death on snow. Zombie does not flail.

What actually happened was...:
Zombie jumped around and span in a circle. Spawned more zombies in a pit of snow (attached), zombies continued jumping and spinning in circles. Attempted same with no snow, zombies walked like normal.

Steps to Reproduce:
1. Generate a superflat world and wait for snow. (You can also place the snow, but it is untested if this works or not. Also untested in a normal world.)
2. Spawn any mob (specifically tested with Villagers, Zombies, Endermen, and Endermites) on an area where it has snowed.
3. Watch the mob flail around and fail to target you, even in survival.

To clarify, I know this happens to mobs which stand on cakes, sometimes slabs, and fences, but this never happens with snow because it was never considered a block. Perhaps Mojang changed the snow? If so, I don't want to enter a Taiga and fight nothing but flailing zombies and creepers.