The Bug:

The "The Power of Books" advancement is granted despite the said comparator not being powered by chiseled bookshelves.

The said advancement description states that you need to "Read the power signal of a Chiseled Bookshelf", however, the advancement is granted despite the said comparator not being powered.

Steps to Reproduce:

1. Place down a chiseled bookshelf.
2. Place down a comparator adjacent to the chiseled bookshelf.
3. Take note as to whether or not the "The Power of Books" advancement is granted despite the said comparator not being powered by chiseled bookshelves.

Observed Behavior:

The "The Power of Books" advancement is granted.

Expected Behavior:

The "The Power of Books" advancement would only be granted if the said comparator is powered by chiseled bookshelves. In other words, the chiseled bookshelf must output a redstone signal (have a book within them) in order for the advancement to be granted.