Yesterday I was playing on my Shadow, everything was going well, I had just completed vengeance mode when all hell broke loose. The flippers started moving by themselves and the display got all weird and chaotic with random dots lit all over the place.
Uhh Ohh, not good! I turned off the machine immediately. Some weird electrical bug. I lifted up the playfield and opened up the back box. At least I didn't smell anything burning, so far so good. I got my multimeter and turned the machine back on to test the various testpoints on the power board when I noticed that the board was not screwed down properly. Once the board was screwed down securely and grounded properly the problem went away. Strange thing is that I own this machine for a while and never bothered to open the backbox because it never caused a problem up until yesterday. When I bought the machine I visually inspected the boards and played a few games. I might have put on 50-100 games on the machine since I bought it, never had a problem until yesterday.
I just wanted to add this post for completeness in case anybody ever has a similar problem.