Villager Trade Prices After Curing Issue

I was reducing the prices of a villager by zombifying and curing it. After a while i noticed the prices go up for no reason. In the wiki it says that the discounts that appear after curing a villager are permanent. I am not sure if this is an intended feature, but it is very annoying.

To replicate this bug, you will have to:

1. Reduce the villager's prices by zombifying and curing him once,.
2. Trade with the villager a bit. Focus on one trade.
3.  Wait a few minecraft days, and the price of the book should go up by 1, 2 or more emeralds.

I used 2 villagers that are at Master level. Maybe this can be important as well.

On the images below, you can see a enchanted book go from 3 to 5 emeralds. I also cured the villager again when it had the trade for 5 emeralds, but the price didn't change.