No Farmers in Villages

When you start a world in Minecraft, the NPC Villagers spawn in their villages in a certain way. You get around one farmer/brown-robed villager for every house, in addition to other villagers that spawn depending on the type of house generated. Not anymore, though. I started up 3 new Superflat worlds, and none of the villages had ANY brown-robed villagers. They were all replaced by priests and librarians. The spawn egg still spawns them, though. Please fix this!