What you could have is a problem with codensation. If it's conduit, your (his) warm moist house air travelling through the cold attic will cause water to form in the pipe and drip down. If it's romex, I don't know, but I wouldn't rule out condesation.
I have seen this many times where the water shorts out the smoke. That's why I never run conduit straight up out of a wall or ceiling box and extend it into open attic. Always follow the contour of the insulation for as long as you can. If you have to up to an attic light, put a few 90's before you fly. This way any condensation will have a chance to re-evaporate as it warms back up.