Villagers Always Generate and Get cured from a zombie villager with XP already gained

Whenever a villager spawns in a village or igloo basement, or is cured by a zombie villager, the villager is given a small amount of XP towards his trades. This means that said villager is not able to change profession, as the game thinks you already traded with them at that point in time and will not allow you to change the profession using work station blocks.