After the reg file fix above, I again ran TweakUI's Repair Icons feature because I had a few remaining issues. The Control Panel icon was missing, dvd drive icon was missing, and a few others.
I read your post again, Medfly, and have to say that my system is exposed to a great many hazards but I do my best to maintain it. I work on sick computers almost daily so try to maintain mine in the best shape I can. It was, however, a very old install of SP2 and some registry issues could certainly have been there. It might also be this particular combination of hardware and software is one you have not encountered - and I would bet on that.
I did note that a few others have reported similar issues, at least when they had installed the RCs.
All is well for now. In any case, I have a full Acronis backup of the SP2 install so there is little risk.