What "fuel cut-off" do you mean? Normally, with any prop aircraft, you cut the engine by reducing the mixture control to full lean. The fuel tank selection valve is turned to "off" after the engine quits. This is a safety precaution -- if you do it the other way, whilst the engine might suck some of the fuel out of the pipe line after the valve is off, it cannot take it all out, and that leaves a dangerous situation where the engine could start up just if the prop is moved.
Regards
Pete
The Cub is apparently different, Pete (according to A2A, I have no real world experience of the Cub). There is no mixture control, so the engine is normally shut-down by switching off the magnetos. The Accusim module will allow the engine to run for a few moments if the fuel is shut-off, simulating the burning of the fuel in the carburetor. That, I guess, is why operating the fuel cut-off valve doesn't get noticed by FSUIPC.
Regards,
Norman