Put the summary of the bug you're having here

What I expected to happen was...:
When a villager levels up it sometimes gets a new enchanted book trade

What actually happened was...:
It gave me the same enchanted book from an earlier trade

Steps to Reproduce:
1. Get a librarian villager
2. Level it up
3. on the rare occasion, it will repeat the same enchanted book from an earlier trade (ex Silk touch and then Silk Touch)