Do you happen to have an alternator installed instead of the OEM generator? It's possible to get a feedback from the alternator to the ignition circuit that can keep the ignition powered up with the switch off. Not likely, but it's worth checking for stray voltage at the coil during the run-on situation.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!