I've noticed random incorrect highlights of the opponent yellow (leftmost to me) play area during my turn. Often it happens on my first turn in a new game, and then sometimes once or maybe twice more during the game. I'll select a card and my play area will light up and so will the yellow play area of the opponent, a circle will light up over there (on my upper left). It's not on the discard pile though, it's where they place a card in that column.