I was testing the 20w16a version and while playing, I encountered a bug. I was trying to get different trades for a librarian villager and while continuously destroying the work block and getting different trades, it just stopped working and he stayed a librarian after the work block being destroyed. I waited for a while to see if he would change back and see that his work block was gone but nothing happened. I tried it with a different villager and the same thing happened. Not sure if this is supposed to happen or it's bugged.