Passive mobs won't spawn

If all passive mobs like cows, pigs and so on are killed they won't respawn. In previous versions there was the maximum amount of passive mobs in the spawn area (all the loaded chunks plus two on each side) which blocked all the other passive mobs from spawning.
I hope it is a bug!

*Nevermind it works passive mobs will spawn if there are no others in the spawn/loaded chunks.