The comparator remains activated even when the chiseled bookshelf has no more books in the block
Step 1: Place a book in the chiseled bookshelf with a comparator behind the bookshelf
Step 2: remove the book from the bookshelf and see that the comparator remains activated
Duplicate of MC-256486, WAI, explicitly mentioned in the changelogs: "comparators output a signal strength equal to the last slot interacted with", that means that once you add a book, it never turns back to 0.