You can continue the molding over the bookshelf. Eliminate some books and add pictures, sculptures or knick knacks.
Go to home depot or Lowe's and get the corner piece. Attach butt up to existing molding. Make sure it's the same style. As you look up at it when finished your right side should fit to the curve etc of existing molding and the left side should be flat at the end.
It should have stopped at the bookshelf maybe?
Nevermind. I see it did on the other side. Oh well. Not sure how this can be accomplished.
I think the only way to fix this is to remove the top of the ‘face frame’ (the part that butts against the ceiling) and install a wider piece so the crown molding will have something to butt up against.