I just jumped into the build and there doesn't seem to be an issue. Are you clicking on the pieces or the board squares under the devils pieces. You must click the square below the piece. I should make that more clear, my apologies!
Ah yeah, seems like I was clicking on the pieces instead of the spaces. Did run into a coup-le of weird bugs - one of my knights just froze in the center of the board and the other knight was somehow commandeered by the devil when he castled with it. The Devil then carried on using my knight as if it was a rook!
It's a cool game though. Would recommend adding subtitles to what the Devil says at the end because I couldn't make out any of it!