Using Vista x86 and the latest version of CC.
File extensions that have only the sub-key UserChoice are being flagged as unused file extensions. They are not. I think UserChoice is new to Vista.
Example:
Windows Registry Editor Version 5.00
[HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\FileExts\.wmp]
[HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\FileExts\.wmp\UserChoice]
"Progid"="mplayerc.wmv"
oops didn't see the bugs forum. Sorry.