Villagers reset trades after locking one

Steps to reproduce:

 

1. Lock any villager profession by buying anything from him (let's say you bought emeralds by giving him carrots)
2. Now Save & Exit
3. Open your world again
4. Go to the same Villager and there is a chance his trades have changed (buy emeralds for potato now for example)

As I said, there is a chance, this has happened to me 3 times now but only with specific villagers