Electrical Autonomous Headlight Operation

Here's the deal...I have a 2006 GT that just developed a dead battery while I'm at work. The headlight switch was in the 'off' position, yet the driver's side headlight is on and will not shut off. Neither the parking lights, tail lights, or passenger's side headlight is on. This has happened just once before, about 20 months ago, and after taking it to the Ford dealership they "weren't able to replicate the problem." Any clues? I'm at a loss.

Unfortunately, by the time I discovered it,the battery was too far gone to start the car and I didn't have time to find a charger. Once I was off work it had completely died and once I got it charged up and running the light was no longer on. Guess I'll have to wait till the next time it decides to freak out.