I checked the wiring diagram for the '81-'84 twin shock bikes, don't know if the mono shock bikes are any different wiring wise .
There is a lighting relay under the seat, it turns out all the lights when the starter is being used .
It looks like it is wired 'hot ' for the load circuit, powered all the time from the battery .
I don't know if your bike has the same looking relay, but it is a metal case relay on my twin shock R65's .
You could try tapping on the relay case with a screwdriver handle and see if the lights go out the next time this happens .
Correction, the relay is under the fuel tank, also there may be another large metal case part in the same area, it's the voltage regulator .
I don't know if the mono shock bikes have the upgraded red and black plastic case regulator .