1. In a newly discovered desert village I locked some villagers up separately with beds and lecterns and kept breaking the lecterns until they had great trades (Mending, Looting, etc). I expected them all to keep their trades but the ones I didn't trade with right away changed their trades. I knew that their profession (and trades) would be locked once I traded with them, but I didn't know that villagers with a profession could change their trades before I traded with them.
2. ...
I am a bit frustrated with this village. It originally had many nitwits, which is why I locked up the "regular" villagers who can take on professions to keep them safe. I only had one farmer, but I figured that the nitwits would breed and produce more villagers who could become farmers and be a source of gems. Unfortunately, while I was busy locking up the productive villagers and trying to get some farms started (there was only a single farm with 4 blocks of farmland and no dirt anywhere when I arrived), all the nitwits disappeared. I slept every night when in the village so I assume they all fell into surrounding deep cave holes and got themselves killed.
EDIT: I solved my second problem. A villager was standing on a decorative step in his house and therefore couldn't take on any profession. I broke the step and he turned normal again.
Singleplayer 1.15 game:
1. In a newly discovered desert village I locked some villagers up separately with beds and lecterns and kept breaking the lecterns until they had great trades (Mending, Looting, etc). I expected them all to keep their trades but the ones I didn't trade with right away changed their trades. I knew that their profession (and trades) would be locked once I traded with them, but I didn't know that villagers with a profession could change their trades before I traded with them.
2. ...
I am a bit frustrated with this village. It originally had many nitwits, which is why I locked up the "regular" villagers who can take on professions to keep them safe. I only had one farmer, but I figured that the nitwits would breed and produce more villagers who could become farmers and be a source of gems. Unfortunately, while I was busy locking up the productive villagers and trying to get some farms started (there was only a single farm with 4 blocks of farmland and no dirt anywhere when I arrived), all the nitwits disappeared. I slept every night when in the village so I assume they all fell into surrounding deep cave holes and got themselves killed.
EDIT: I solved my second problem. A villager was standing on a decorative step in his house and therefore couldn't take on any profession. I broke the step and he turned normal again.