This just happened to me in my Father-in Law's car! I moved the damn thing 20 feet, and in doing so, accidentially shifted into the overdrive gate, and took in right out. Then shifted into park but the button and key were stuck.
My Father-in-Law thought I broke something, and took the car out and drove it around with no luck. It wasn't until we wwere back out in the driveway, and I remembered the "accidental" overdrive shift. He repeated the shift into the overdrive gate, and then back to park and "voila" problem solved!
This can be caused "accidentially" if the shifter is pushed into the "OVERDRIVE" slot. If the button on the shifter handle does not release when it is pushed into PARK, just moving the shifter into the overdrive slot "AGAIN" which should cause the button on the shifter to pop out as usual, and in turn, allow the ignition key to release.