Bob, the distribution spider has a spring that is supposed to remain closed when insufficient pressure results from mixture cutoff.  It has some hysteresis so once closed it may not open up with the same low boost pump on while it might remain open with the boost on low.  However, it should shut off with no boost pump and ICO.  That's my recollection of how that spider works on the Continentals.  I think most will continue to run with the boost on low and ICO.