Here is what I think is happening. If you look at Janaka's picture of his FPR, I'm assuming you have a feed from the tank coming in on the left, the return on the bottom, and the right port going to the dead ended fuel rail. If this is the case as it is with Clive's, if the pump were to pull any amount of air, if the bubble were to get past the FPR, the only place it would b dispersed would be through the injectors causing a major stumble.
Does that statement make sense?
Joe