I was wrong - the magic continues

I have no problem admitting that I was mistaken about the cause of the scary light syndrome in the den. No one went near the garage, or the remote controlled door openers yesterday evening and still the lights came on.
First the built-in lights came on at 7 PM, then the chandelier came on at 9:56 PM. Then I went to bed, leaving them on. They could burn themselves out for all I cared at that point.
But magically at 12:20 AM when Steven turned the outside lights off, all the den lights went off, too.
Now that leads me to believe that there is some complicated light sensitive stuff going on here that is controlled by the outside light switch. But it must also be timer controlled because I've tried turning the outside lights off before, many, many, many times.
The outdoor lights aren't on a timer (at least we've never discovered one) nor are they on a light sensor (although I've often thought they should be). So WHY?
Why is this happening and what can we do to turn this into a plus? Lights that go on and off when we're not home - that's an anti-burglar system.
And if we can't do that, at least tell us how to make this stop. For good.