Quoted from Bubbatom:
So, I was tightening a flipper solenoid on my RS with the game off (not at the wall though) and accidentally let the screwdriver touch one of the solenoid contacts. I was very surprised to see a bright spark when the two touched! I've been doing repairs on this and the last machine with the game off, but still with the switch on the wall on, is this a good idea? It appears not!
I always use only the game switch and never have a problem, it sounds to me like you just experienced the games power supply storing a charge in the solenoids power section capacitors. No worries, just allow the game to self discharge for a little while before working on it if you are concerned, and stop throwing your tools around