Now that hoppers can interact with chiseled bookshelves in 22w44a, the redstone behavior no longer matches the intended behavior from the announcement.

Setup

1. Place a chiseled bookshelf over a hopper. Set up a comparator to visually measure the signal strength from the bookshelf.
2. Power the hopper.
3. Fill all hopper slots with plain books, so it can take in only more plain books.
4. Insert books into the bookshelf in the following order: Protection I enchanted book, plain book, plain book, Protection II enchanted book, Protection III enchanted book, Protection IV enchanted book.
5. De-power the hopper. Observe comparator output as the two plain books are removed.
6. Add two books-and-quills to the chiseled bookshelf, observing comparator output as this is done.
7. Remove the books from the bookshelf.

Actual behavior

At step 5, the books are removed from slots 2 and 3. Comparator output indicates 6 after the first removal, then 5 and then 4 after the second. Block texture is no different from when slots 5 and 6 were empty.

At step 6, the books-and-quills are inserted into slots 2 and 3. Comparator output indicates 5 then 6.

At step 7, we get back the books in the following order: Prot IV, Prot III, Prot II, book-and-quill, book-and-quill, Prot I, confirming that the two books-and-quills were inserted into slots 2 and 3.

Expected behavior

There are several ways this could work to be consistent:

• The comparator output indicates slots 2 and 3 when slots 2 and 3 are the last interacted with, as it is currently defined. And ideally the block texture would visually indicate which slots are empty too.
• The hopper works more like "remove book from slot 2 then shift all books over" so the empty slots are always at the end. In that case the comparator output should have been 5 (not 6) after the first removal (since the last action was moving the book in slot 6 to slot 5), the output after the second removal should have immediately been 4 (not 5-then-4), and the order the books are retrieved in step 7 should reflect the books-and-quills having been inserted into slots 5 and 6.
• The hopper can only take from the last filled slot. Although IMO that would be much less useful behavior.
• Redefine the redstone behavior to indicate fullness, like other containers, instead of "last interacted slot". And still maybe adjust the texture to indicate which slots are empty.