Custom villagers don't lower their prices

I spawned in a custom villager that offered enchanted books and stuff (all vanilla books, so no, like, Sharpness 10 or anything), and the trades looked a little something like:

28 Emeralds + 1 Book = Sharpness 5

14 Emeralds + 1 Book = Efficiency 5

1 Book + 26 Emeralds = Unbreaking 3

(the order for the last one was a mistake on my part)

My Hero of the Village effect lowered the prices in terms of emeralds for all the trades except the one where the books came before the emeralds. That one was completely the same.