ROB: The Magen Avraham explains Rashi exactly as I wrote, that one must leave a gap for air circulation so the fire will not go out. His pshat is brought in Mishna Berura, Pri Megadim, Shulchan Aruch HaRav, etc, and no one seems to argue.
The only other pshat I found in the Gemorra is the Meiri who explains on 107A that the Mishna is brought there in the context of ??? ????? ??????/?????, which certainly would not apply to turning off the gas intentionally.