I have just tried the latest FSUIPC and have no problems whatsoever.
I had already reported this to the developer and he has asked for the following information should you still be having a problem.
1. How are these users starting FSUIPC7 - is it auto-started (recommended) or are they starting it manually, and if so when (i.e. before or after MSFS is started)?
2. Are these users using a registered/licensed version of FSUIPC7 or an unregistered/freeware version?
3. I will need to see a log file with logging for Buttons & Keys activated.
I can confirm the same issue and it's intermittent. It just happened and I exited FSUIPC and PF3 and restarted both and now it's working. I've also seen weird key presses coming in from GSX to load the PMDG 737 so I'm not certain its not also a GSX issue too.
Mike T.