My 2002 Impreza quite often will not give up the key.  When shutting the engine off (car in park), the key sticks in ACC.  It can be started and driven but again on stopping it won't give up the key.  Or it does.  It used to be a rare occurance and always with my key, not my Wife's.  the problem is getting more and more frequent.  Jamming on the brake pedal used to make a difference but not anymore.  It doesn't do this all the time, but we never know when its going to happen.  Help!!!

The interlock switch in the center console may be sticky. When the selector is moved out of park the switch activates a solenoid in the column which keeps the key from turning back all the way to Lock.

 

Usually the cause is a drink spilled in the center console. Pull up the console trim and clean everything around the shifter assembly.

 

Less likely but still possible is the solenoid in the column is getting stuck.