[Zope] MSIE 6 not opening MIME attachments

I'm trying to send a CSV via a python script. My problem is in IE 6, if the user clicks on "Open" instead of save from the dialog that appears, Excel will launch, but not find the file in the Temporary Internet Files folder. Clicking on "Save" then opening the file manually works just fine. Is this a problem with my response headers or an IE bug? Here are the headers I'm sending: response.setHeader('Content-Type', 'text/csv') response.setHeader('Content-Length', len(printed)) response.setHeader('Content-Disposition', 'attachment; filename=%s' % filename) return printed