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.
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We're tracking this issue in MCPE-117852, so this ticket is being resolved and linked as a duplicate.
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