Hello, I'm not sure if this is a vanilla issue, but I notice that whenever I try to place books on the tall, narrow bookshelves, the books placed on the left portions of the shelf end up sinking through the shelf. Not only books, but virtually anything I place on the left portion of those shelves ends up sinking through the shelf base and ends up stuck inside the base of the respective shelves. In the case of books, they sink in like quicksand, leaving them half in the shelf base and half in the shelf itself.
I'm not using any bookshelf altering mod save Auto Book Placer.