1999 Buick Regal Ignition Key sometimes is locked in igniti

When you park your car and turn off the key and try to get it to the lock position, You can not get to lock. The engine shuts down, but now able to remove key. If I go back to the car in anything from a few minutes and do a slight flip to start and lock, you can then remove the key from the ignition switch. The dealer thinks it is the shifter or a micro switch that senses the car in park position. Do you think it is in the shifter or might it be a bad or sticking ignition switch. Thank you.