the chiseled bookshelf stays active when the book it taken y a hopper

I was experimenting with the chiseled bookshelf and hoppers to explore possible secret door builds, when the redstone stayed active after the mine cart hopper took the book, I tried moving the block with a piston to see if that would fix it; it did not, the redstone did turn off when the block got pulled away but when I put it back the redstone reactivated as though there was still a book inside when in fact there was not a book inside. I do not know if this was intended but that is what happened.