Internet Explorer, Windows 7, Zip files not downloading correctly

Ok, I'm not sure if this is exactly the place to post this, since I know RDF and Bitcache are connected to this, but I'll post here anyways.

I am running File Framework as a file sharing (mods for a game) database at http://www.runicgamesfansite.com/torchlightmods/ . I recently had a report that someone was getting a strange problem when downloading zip files, but only when using IE 8 in Windows 7. Any zip file he downloads has underscores instead of spaces in the file names, and when unzipped instead of showing the correct contents, it shows an unassigned file type with the same name as the .zip file it unzipped from. When renaming the unassigned type to have a .zip on the end, only THEN does it unzip to show the correct files. I have managed to duplicate the error, but I'm not sure what is causing it.

I'm not sure if the problem is in IE8, Win7, or specific combinations of the two. It might even be something strange in the IE8 Browser settings. I'm going to try to get my users to test this more, and will update when I have more information, but for now I thought I would make you aware of the problem and see if you have any insight.