One of my previous room mates was really sensitive to it and would get headaches from the smell. I could only test gas guns indoors when he was in class and there was enough time to vent the place before he got back.
Smoking shouldn't be a problem as the gas concentration required to become explosive is quite substantial. As long as you don't hold open flame to the mags while you fill them or to the gun while it fires you are probably fine. I see people at games filling mags while smoking all the time, I have no idea if the propane concentration is high enough in the immediate area to worry about but in three years I have seen countless people doing it and never even heard about an accident.