MarketPress downloadable files are corrupt after download

We have MarketPress up and running and even made a sale! We have tested a .pdf and a .ZIP file. After the user makes the purchase and downloads the file, they find that it is corrupt and cannot be viewed or opened.

We have verified that the files are OK after uploading them through the media uploader. We thought the media uploader was doing something to the files and we might have to FTP them to the site.

So, somewhere between the user hitting the Download link and arriving at their computer the files become corrupt. We noticed that MarketPress renames the files to the Product title. Would that have anything to do with this? Anyone else had this problem? What am I doing wrong now? (it's gotta be me, it can't be this awesome software ...)