Describe the bug

1. Broken trade with a farmer. 6 emeralds for 1 emerald.
2. Librarian doesn't upgrade his level of trading after my trade with him. I used "bugged" emeralds from the previous step.

To Reproduce

1. Trade with a farmer. (look at the screenshot)
2. Trade with a librarian. (look at the screenshot)

Expected behavior
A librarian should upgrade his level of trading (not only him but I have an issue with him). He has an item on his belt that changes, which indicates a level increase (look at the screenshot). But it doesn't change.

Screenshots
A farmer

This thing on a belt that doesn't change

A librarian

Info (please complete the following information):
3.0 v4
Singleplayer:
3.0 v4

Additional context
Seed : 3341179550070224022
Seed screenshot

Location 1586, 73, -174

villagers level up from village rep

Guess it's different from 2.77 and vanilla minecraft. But I already have 186 rep and trades don't change at all. Level doesn't increase.

Librarian actually doesn't have any more trades at all. We'll add more later based on rep. I also removed the emerald to emerald trades, so it will be fixed in beta 5