What I expected to happen was...:
Books disenchanted/reverted back to normal books using the grindstone would stack with other books that had never been enchanted.

What actually happened was...:
Disenchanted books refused to stack with other non-enchanted books, both those crafted in version 1.13.2, and those crafted after the update to 1.14.

Steps to Reproduce:
1. Craft two books.
2. Enchant one of the books.
3. Disenchant this book using the grindstone.
4. Put both books together in your inventory. They will not stack together.