Yeah, the word "Lecture" is behind the puzzles upper left in the previous screen and prevents touching puzzle pieces in the area it would be in due to making it come up with info on the stealth skill. You literally cannot complete the Art of Discounting puzzle because two pieces are in that spot.
To get by this puzzle, however, I had to click on the outside edge of the piece where the word 'Lecture' wouldn't be. Just keep trying to drag from the very edge of the piece. There is a sweet spot. I wanna say it was the bottom right corner?