Do NOT buy or sell enchanted books using shop chests Minecraft item codes do not have any way of distinguishing enchants on a book (all items 403), so regardless of whatever book is in the chest, the player will buy a blank enchanted book Trade them as you please!
It means that the chestshop plugin doesn't know how to deal with the selling and buying of enchanted books so it glitches out and ruins the enchanted book itself.
You can now buy/sell enchanted books! Enchanted items now have the item id followed by "#<x>". Eg. Unbr III eff IV diamond pick is 278#a, so a book could be 403#4