Toymaker, I think that many inhibitors change the PH, or tie-up Oxygen ions with heavier elements, metals or whatever, which precipitate as solids when the water boils-off.... But I am not a chemist, so do not really know what happens. I agree that miscible liquids can boil at a "mutual boiling point" as you describe, but I don't really understand this at all? e.g. salt raises the boiling point of water... but: surely Distillation is the removal of the lower boiling point "fraction" from the mix? Otherwise how would fractional distillation work? - Different temperatures to boil-off different fractions of the mix? Anyone with a Still knows to control the temperature to boil-off the Ethanol, while not boiling-off the methanol, and water, when removing the spirit from the fermented mash. Of course, in your flash boiler, you are exceeding the boiling point of all the various fractions I guess, if using an inhibitor, so everything is passed to the condenser to mix again.
K2