2005 Chevy Impala Wiper malfunction

Engine Mechanical problem
2005 Chevy Impala 6 cyl Front Wheel Drive Automatic

My wife has a 2005 Chevy Impala with a windshield wiper problem. One day this winter she was using her wipers and when she shut them off instead of returning to the "store" position at the bottom of the windshield they went to the halfway mark (in the middle of the windshield) and stopped. I cleared away all of the froxen material under the wiper arm but they are still stopping in the wrong position. Any ideas. Thanks for any assistance you can offer.