The interior lights in my car (climate control, radio, dash, etc.) all work normal when the headlights are off. When the headlights turn on, all of the interior lights mentioned previously turn off leaving a completely dark interior.
Is it possible that you have the dimmer for the interior gauge lights turned all the way down?
I would hate to think that I am that stupid, but no I have not checked that. However thinking about it makes a lot of sense now. I have a 2-year old that loves to push and pull all the lever, knobs, and buttons she can get her hands on. I will check that tonight. Thanks for posting.