Good morning, Pete.
You were correct, using v4.939g when I uncheck the 'exclude ThrottleN set' checkbox in the Throttle axis calibration page, the throttles become unresponsive, just like v4.939j and later. without restarting the FSX session, I can immediately re-check the same option and the throttles work again.
In case in matters, you should be aware that I only use FSUIPC for button/key/axis assignments (send to FS as normal axis) and I do not use any of the FSUIPC calibration facilities, which seems to work best with my PMDG aircraft.
FYI, I will only have access to my Flightsim-rig for a few more days (probably Wednesday) before tearing everything down to begin the process of moving my home to Florida - I don't anticipate having it running again until late May. I only mention this because there's no hurry for a permanent solution on my part, and I won't be able to assist in further troubleshooting during this time.