I'm not 100% sure that it is a bug but I know that Mojang fixed a infinite emeralds paradox glitch with librarians where you could cure them and practically get infinite emeralds (by buying cheap bookshelves, breaking them, and selling the books back to the villagers).

Apparently I have found a loophole around this where if you cure a librarian twice, his price for bookshelves drops to 2 emeralds which enables the infinite emerald paradox all over again. Like I said, I'm not sure that it's 100% a bug but I thought I would give a heads up because it is fairly easy to do this to get infinite emeralds. I provided a screenshot with proof.