Internet Explorer and zip-files error

Hi

I have a problem with MWS 7.1.1. If I download a zip-file IE stores it as test.zip.gz. I can extract the original zip-file without problems but thats not the behaviour a user expects. It works fine in Firefox. checking the headers, the response header in IE doesn’t have the line “Content-encoding: gzip”

content part of the IE header:
Content-Disposition: attachment; filename=test2.zip.gz
Content-Type: application/x-zip-compressed; charset=UTF-8
Content-Language: de
Content-Length: 2093

Firefox header:
Content-Disposition: attachment; filename*=utf-8’en_US’test2.zip
Content-Type: application/x-zip-compressed; charset=UTF-8
Content-Language: en-US
Content-Length: 2116
Content-Encoding: gzip

The configuration of mimetypes.properties is out of the box, i haven’t touched this. The line for zip reads:
.zip=application/x-zip-compressed (compressed)

How can i change the configuration in a way that IE receives zip files only and not zip.gz files.

Thanks