When a villager that hasn’t been traded with turns into a zombie, the villager has a chance to have trades different to the profession.

How to reproduce the bug:

1. make a area for villagers (There must be a roof so zombies don't get burned)
2. don't trade with the villagers 
3. Spawn the zombie to turn the villagers into Zombie villagers 
4. kill the zombie
5. Cure the villagers (It's best to separate the villagers with boats and cure the villagers in each boat
6. The some villagers will have incorrect trades

The trades from villagers that were bugged:

1. Fletchers trading emeralds for chickens
2. Librarians trading cooked fish for emeralds and fish
3. Armorers trading bookshelves for emeralds