Summary:
In my single-player survival world, I've been working towards getting perfect enchantments for my sword. In trying to do so, I've turned to villager trading, in which I've been having some problems. What I expected was for the villager to gain the profession, and I would check to see if they would have the book I want, and then I would break the workstation to try again. However, the villagers would lock on the profession, and even though I didn't trade with them, they would keep their profession. I've afk-ed in one spot next to the villagers, broken different workstations in different ways, etc. in order to be able to reset them. However, they never seem to get rid of it no matter how much I try.

Reproduction:
I'd say the best way to reproduce the bug would be to get a group of villagers, (approx. 5 - 10)  and have some villager have locked in Librarian villagers and then keep resetting them,  until they start locking up.