I added lava to my Leatherworkers cauldron and he disconnected from it and refused to reconnect. I went into creative to play around with it and it seems to be a consistent problem. Adding water or potions does not have any issues. I also tried different biomes to see if it was only one type of villager and it made no difference.

To replicate - have one villager with a bed and a cauldron, wait for him to connect to cauldron, then add a bucket of lava to the cauldron.