During normal game play I stumbled across a freshly generated village and decided to check the trades of the librarians as I passed on through, and noticed a librarian with the trades of a leather worker.

The only way I can think of to reproduce the bug is by going to the exact same Village (You can see the house that the bugged villager spawned inside in the provided screenshot with coords and seed)

Seed: 6078546101329128515
X=29
Y=72
Z=-2,481