Villager trading

I'm playing with Minecraft Java edition 1.14.2 in Sienimaailma.net survival server with Windows and I found a villager trading bug. The villager sell two enchanted books. A Mending and a Luck Of The Sea 1. When I buy the Mending book it change to Luck Of The Sea 1 book when I put it in to my inventory. The villager have been zombie villager before but I heal it to villager.