The kind of air lock you are talking about is due to the air pocket being pushed thru the system to the pump. At the pump you have trouble because the pump vanes/pistons/rotors/whatever depends on the fluid to seal up the clearances and gaps in order to create the pumping action. With an air pocket in the pump, it has trouble priming and will just spin without moving fluid. This brake system we are talking about has nothing to do with pumps since the bubble is a long way from the master cylinder (pump).