One of the mods I have in my pack is FatherToast’s Lost Books. Occasionally, when a mob is killed it will drop a written book (minecraft:written_book) which usually contains a short story or procedurally generated text. If you choose to collect these books, after a while you wind up with a lot of them, and since they don’t stack they can take up a lot of space in your chests.
I remembered reading a while back that you can use GT6 bookshelves to increase the level of an enchanting table if you fill them with books, so I figured this would be a pretty good solution both for storing the books and making the enchanting table more powerful. But I noticed that the enchanting level wasn’t going up, even though the bookshelves were full of books on both sides. Then I tried replacing the written books with normal empty Books, that raised the level of the enchanting table as expected.
I wasn’t sure if this was a bug or intended behavior but I figured I’d make a post about it just to clarify either way.