I was giving a villager a profession as a librarian and the villager randomly became a librarian even though I never put down a lectern. I typed /data get entity [entity] and it said the villager had a jobsite at [x] so I went to the jobsite based on the coordinates. I found it was a lectern next to a villager that I locked the trades of. I got the entity data of that villager and the jobsite he was connected to was the same lectern. I broke the lectern and placed it back down and the villager with the locked trades kept his profession, and the other didn't lose his profession. The lectern was within ten blocks or so of the villager without locked trades when he took the profession. Could making the villager unable to pathfind to the jobsite fix it? I even tested it in a different world and the same thing happened.

Note: The villager that randomly took the profession was in a minecart. Not sure if this makes a difference.