IE7 on Vista: File extension stripped when using View Source

I just set up Windows Vista x64 edition and am using Internet Explorer
32-bit and configured the registry to use an alternate text editor to be the
View Source editor.

I'm finding that the file extension is being stripped when executing View
Source from the browser. So the text editor keeps pulling it up in plain
text rather than with HTML color coding. Since my text editor is Visual
Studio, which I like to use because I can click on the Reformat button to
"pretty" up the source code instantly, opening up the file without the
extension disables such functionality.

This seems to be behavior specific to Windows Vista. I had IE7 running on
Windows Server 2003 and didn't have this problem; when I executed View
Source it always retained the file extension so my View Source editor always
saw .aspx files as .aspx rather than extensionless.

Is there a way to restore the file type?

I'd even be willing to go so far as to build my own EXE to
copy-and-rename-the-file-and-open-it-in-my-editor, but it would need to
otherwise know the MIME type (no sense in renaming a JPEG file to have an
..html extension!), and I don't want to actually read the file's contents to
accomplish that (too hard and flakey; any file can be malformatted).

Thanks,
Jon