Slimes won't spawn naturally.

Yesterday I updated minecraft to 1.6.1 version. Back then everything was normal.
Today I created my first survival map, and found some donkeys, i went to a swamp nearby to get slime balls for leads, and waited till dark. No slimes, it wasn't a new moon, so it should have spawned some. I camped there for 2 hours (the whole moon cicle) and nothing. Then I created a creative map with large biomes, absolutely no slimes on the whole spawpland, but there were other agressive mobs there.
They still can be spawned by eggs.