Auto headlights won't shut off - ideas?

I noticed today, driving in bright sunlight, that my automatic headlights were still on. This hasn't happened before and I know they were working last week. I'm not sure where the sensor is...I'm assuming it's with the rain sensor attached to the rear view mirror. If I'm right about the sensor area, it seems clean.

Is this a common problem? Is there something I can do to reset the sensor or is there no adjustment?

I'm under warranty (barely) but was curious as to whether this problem is other than a part swap by the dealer.

Thanks,

RB