[ByronRACE]

The chassis of the fuel pressure gauge should be vented to atmosphere.

This is likely a detail that the knock-off manufacturer failed to copy. Drill a pinhole in the gauge body somewhere below the fluid filled gauge face and it shouldn't do that anymore. That is, unless the entire gauge is filled with fluid...if that's the case, it's a design flaw.

The mechanical gauges have metal bellows in there that uncurls with pressure and moves the needle. If the pressure inside the gauge housing builds with temperature, the uncurling effect will be lessened because the differential pressure is lessened.

Typically just the face is filled with fluid; to dampen the needle movement.

Byron