Try this next time: with the gear shift in park, engine running and unable to shut it off and get the key out, try hitting the bottom of your closed fist on top of the shift knob, then see if the key will turn all the way off. Don't hit it too hard though, you might break something in the shifter or your hand!
The dealer's service writer told me about this when it happened to my wife at the local wally world a few months ago. He said there can be a very slight misadjustment with the shifter, shifter button, cable, and ignition switch. I lubed the cable not long ago when I had the console out for gear indicator bulb replacement and the wife reports it's doing much better.
JR