Yeah, I experienced this indefinite breathability under water during 14w07a.
Yes, I've seen this too. It was in 14w06b as well. If I hit a zombie or creeper in the water, they would practically just "stand" there.
I also noticed enderman don't teleport out of the water right away. Makes it super easy to kill them.
What a noob, I am.
Yeah, I experienced this indefinite breathability under water during 14w07a.