Mobs aren't swimming/bobbing in water

It seems mobs (Cows, Sheep, and Pigs) aren't swimming/bobbing in water at least since Pre-Release one. I discovered this in making a micro-breeder for cows and they wouldn't bob in a 1x1x2 area. I have confirmed this is the same in any size pool of water (1x2x2, 2x2x2, etc).