Sure is hard to get fuel to run against positive air pressure
Not to mention the net flow rate of fuel in the opposite direction, adding a component of suction into the pitot tube vent. I find it pretty hard to believe that any fuel vapor could cause a visible cloud. If that much fuel was somehow being drawn out, the pressure drop in the tank would surely cause the pump to cavitate and probably put out the stove...
Just my $.02 (in canadian funds...)
Kelly