Here's a simple and stress-free way to look at the situation:
Each vacuum element---receiving vacuum, not receiving vacuum, leaking vacuum---has a diaphragm and control rod that is in a position of one sort or another at any given point in time. The attached flap is thus in a position of one sort or another at any given point in time. Added together, this means that so long as there is air flowing through the system, the air will exit at a variety of locations. The air flow exit locations may not be what you desire, but the air will exit nonetheless. To my way of thinking, not a particularly onerous issue.