1999 Plymouth Voyager. When the headlights are turned on, the AC/Recirculate buttons won't work. Pressing the buttons won't turn them on or off (if they're already on). Turn off the headlights and they work fine. Any clues or theories about this would be appreciated.

 

Actually it's slightly weirder even than that. The controls (A/C and recirculate) actually function when the headlights are on, but their indicator lights don't change. With headlights off, they behave normally.