Villagers spawn the same at first spawn

Villagers all spawn as similar types. They usually spawn in accordance to house type, however they now spawn as all the same or similar. I was looking for some Villages, when suddenly I noticed that the Villagers were all Farmers! I went to another Village and lo! they were all Blacksmiths. In another they were all Librarians. How to spot this bug:
1) Find Village
2) Check that Villagers are all the same or nearly, regardless of house type.