When any kind of tool that has been renamed is put into a grindstone in the top slot, the output item keeps the name. However, if you rename an enchanted book, the name is lost. It just becomes 'book'.

Steps to recreate:

1) Name a sword in an anvil

2)Name an enchanted book in an anvil. The specific kind of enchanted book does not matter

3)Put the sword in a grindstone and take it out, taking note of its name

4)Put the enchanted book in a grindstone and observe as the name is lost