If you remove the ingredients from an enchanted item BEFORE removing the enchanted book, the item is immediately uncrafted and you can't get the book.
Also, while uncrafting an enchanted item: Removing a book, then exiting the GUI, allows you to keep the book AND item. Repeating the process over and over will yield infinite supply of enchanted books.
When using the Advanced Uncrafter:
If you remove the ingredients from an enchanted item BEFORE removing the enchanted book, the item is immediately uncrafted and you can't get the book.
Also, while uncrafting an enchanted item: Removing a book, then exiting the GUI, allows you to keep the book AND item. Repeating the process over and over will yield infinite supply of enchanted books.
*MC - Forge - Uncrafter versions in title