A villager should be able to change jobs until traded with, and then when the villager has been engaged with, they are locked into that job. For example a journeyman should not be able to change from being a leatherworker to a cleric. This happened to me however, as my journeyman leatherworker that I was working up to be a master trader suddenly, despite the cauldron job block not being deleted, changed into a cleric, for no apparent reason, and I have been unable to change the villager back to a leatherworker.

Any help would be greatly appreciated.