2009 Kia Optima parking lights on

I drove my car today at 7am. Then locked up the car and parked it at home. The keys in my house and no one home. When I left to go somewhere with my husband in his truck, I walked right by my car. When we backed up, I was facing my back end. No one noticed the parking brake lights on. I add all this to say they were not on when we left. When we arrived home, my back lights were on and the parking lights were on in the front. The keys were in my cabinet in the house. No one was home and no one around. What would cause this?