With Chrome 12.0.742.112, if I redirect with the following headers:
HTTP/1.1 302 Found Location: http://0.0.0.0:3000/files/download.zip Content-Type: text/h
I experienced this problem when serving up a PDF file (MIME type application/pdf) and solved it by setting the Content-Disposition header, e.g.:
Content-Disposition: attachment; filename=foo.pdf
Hope that helps.