Librarian villager refuses to trade enchanted book, but gives ghost item when shift clicking (on server)

I am trading with a librarian villager for a Mending book, but he refuses to sell it to me. I can shift click the item into my inventory but it gives me a ghost version of the item. Video: https://youtu.be/uVcAvlBzO98

What I expected to happen was...:
The villager would trade the mending book to me.

What actually happened was...:
The villager traded a ghost item to me, when I tried to pick it up in my inventory the item dissappeared.