Thanks once again for the responses. I do appreciate the work you guys are doing.
Just as a further feedback:
The Kindle will not reboot successfully. It either gets stuck on ""...wait till your Kindle restarts" or at a blank screen.
I rebooted it using the "magic" restart while connected to the Windows guest, with Mfg Tool running.
Once detected and the "main" profile loaded, it restarts normally and now shows that the firmware has been upgraded to 5.0.4. It then runs fine, with all functions including 3G operating without noticeable problems; unless shut down, from which it again goes to a blank white screen and cannot be re-booted without Mfg Tool.
"Hard" reset - holding down the power button - makes no difference.
Geekmaster, would you know of any reason why this might be the case?