I found a zombie-villager, renamed them, cured them and used a lectern to get a 1-emerald-mending-trade from them. Traded with them and enchanted my pickaxe. After that I stopped playing.

The next day, I check on them and... they're just gone. The villager and the lectern, both simply vanished. Never ever seen that happen, but it's quite bothersome, considering the effort required, especially early-game in a hardmode-world.