Disenchanted books (grindstone) can't be stacked with normal books

What I expected to happen was...:
That I should be able to stack the books.

What actually happened was...:
They don't stack.

Steps to Reproduce:
1. Enchant a book in an Enchanting Table
2. Put the enchanted book into a grindstone and disenchant it
3. Now you can't stack the disenchanted book with the normal books which haven't been enchanted yet.