I have a Scared Stiff that has developed this problem with a few lights in the light matrix. It's a Williams I know, not Stern, but it's the same issue. I've yet to track it down, but it's on my list of things to do. It does this whether I have no-ghosting LEDs or incandescents installed (I tried both). One of the inserts affected is the extra ball insert, which is really annoying to see that flashing when you know there's no extra ball available. Good luck tracking this down.