Shulker boxes only drop in Creative when they have contents (not even when renamed). But taking books out of chiseled bookshelves in Creative always gives you the item, even though putting them in doesn't remove the item from the inventory. Inserting a book into a chiseled bookshelf and then taking it back out duplicates the item when done in Creative. This would be understandable if there was relevant data in the book, but it's not really useful for regular books and for book&quill without any text.