Ghast balls will make fire, even if /gamerule doFireTick and mobGriefing is on false

This is pretty annoying, because you can't extinguish fire in adventuremode, what makes it impossible to use ghasts in adventuremaps. If doFireTick is set to false, the fire will burn forever and won't extinguish on non-burning materials so it is impossible to make a ghast-proof room because there will be more and more fire after every explosion, what makes it impossible to pass such a room.