That's an interesting clue..
I have a couple of questions:
First, is it the filename Screenshot (1,2) that makes it show, or just that it is a NEWLY found file in that directory? That is, if you copy other image files into your screenshot folder, do you suddenly see them?
Second, any change if you restart SC?
Third, did you happen to use recently the new feature in SC, under View ->Toggle standalone screenshot window (i once saw this kind of behavior from doing that)?