1. Craft a new book. It's a book called "Book".
2. Enchant it. It's an enchanted book called "Enchanted Book".
3. Grindstone it. It's an UNenchanted book called "Enchanted Book".
See attachments for a visual explanation.
Seems to be caused by the fix for MC-148529.
Linked issues
is duplicated by 6
1 more links
Can confirm.