When find a trade i want with a villager, i make one trade to lock that trade. I go to relocate the villager, and when i pick up their work station they lose their job: changing their trade. 

They still have the experience gained from the one trade i did, just different trades.

Villagers in general are pretty buggy right now. I have a library that has the trades of a farmer. He lost his librarian job when i picked up the lectern and linked to a composter that was connected to another villager.