I haven't had this problem (yet) but I've heard about it a lot; enough that I changed things around so now I turn my machine on and off with a power strip. All my sewing task lights and my machine are plugged into a power strip that I zip-tied to the leg of my sewing table, so now everything goes on and off with THAT switch. No way my machine can start up on its own with that setup! And with all the lights, it's easy to see if I've wandered off and left my machine on, even if I can't see the screen.
I've had my 6600 for 2 years; maybe I should be proactive and see how hard that pedal is to open up...