Fuel pressure momentary drop after boost pump shutdown

[jdeas]

A friends plane is having occasional momentary fuel pressure drops after turning off the boost pump. I think we all see fuel flow bumps as the fuel lines between the boost pump and mechanical pump go from pressurized to suction but in my case I never see the fuel pressure drop below the mechanical pumps normal output.

My speculating..

The boost pump is a Andair unit with a built in bypass and pressure relief valve. On shutdown the built in bypass valve goes from ~32psi holding it on its seat to a suction. As a positive displacement pump, all fuel must pass via the bypass value. Is this possibly a sticky bypass valve on the Andair pump? Is it possibly the check valve in the mechanical pump?