Villager trades wrong book

Villager offers Mending book discounted to one emerald

Villager also offers Fire Protection I for one emerald

When trying to buy the mending book, when removing it from the trading interface it at first appears to be a mending book, but when moved it turns into a fire protection I book.

If I put 5 emeralds into the trade, (it's undiscounted price), it will take all 5 emeralds and give me the mending book.

This is happening on a server.