When a villager has been leveled up to Apprentice or higher and when you destroy his workstation, he doesn't lose his proffesion. He acts like a nitwit, he goes around the village and explores the village the whole day and doesn't lose his proffesion, which means you can still trade with him. This leads to really buggy AI, such as not going to bed in the night and completely standing still sometimes.

How to reproduce:

Level up the villager to Apprentice and/or higher and then destroy his workstation.