1. By “farmers” I mean all brown robed villagers (ID 0).
2. This doesn’t affect villages in spawn chunks.

I’ve tested this on at least three randomly generated superflat worlds without any preset customization.

Traveling through a superflat world and causing villages to generate makes all farmers who are supposed to be spawned in them pick one of other IDs. This makes the whole village seem infested with one type of villager, while in fact Farmers are supposed to be the majority in any village.

I’ve personally seen villages swarming with white robed Villagers, I’ve seen silver apron Villagers and I’ve also seen black apron Villagers. I haven’t personally confirmed villages with purple robes (Clerics).

In all affected villages there wasn’t a single one Farmer (ID 0) present.

I used to have doubts about this being a random occurrence. I’ve seen it too many times now to be something on my end.