Safari appending .EXE to the end of .PDF

I have had reported on occasions when Safari on Mac is downloading a PDF from one of our sites it will append .EXE to the end of the file. The MIME type is correctly set to be pdf but it still does it occasionally.

I have found http://support.apple.com/kb/TA24293 which seems to indicate that this is a known issue with Safari on Mac however as official as this is (Since it is from Apple themselves) our clients don't seem to want to believe it. So I want to know if there is a solution to this problem?

I say "occasionally" because we have some Macs that this is happening on and some it's not. So maybe it's a setting or something, it downloads perfectly fine in IE, Firefox, Chrome and even downloads fine on mobile Safari. It is just Mac Safari.

HTTP Header: Content-Disposition

Have the server include an additional Content-Disposition header when serving the PDFs:

Content-Disposition: attachment; filename="<MyPDF.pdf>"

This provides the browser with a strong suggestion for the desired filename and suffix. See How to encode the filename parameter of Content-Disposition header in HTTP? for a discussion about limitations and implementing this feature.

MIME Type

Additionally, make sure the server's PDF mime type in the Content-Type: header is set correctly. There are variations in use. application/pdf is the recommended type.

The standard MIME type is application/pdf. The assignment is defined in RFC 3778, The application/pdf Media Type, referenced from the MIME Media Types registry.

Test with curl

Use curl -I http://example.com/mypdf.pdf to test and ensure the correct headers are returned by your server. curl can provide credentials to work as a logged in user.

Potentially related question: When sending headers to download a PDF, Safari appends .html

Just a blind guess:

On the Macs with the issue, install RCDefaultApp, and use it to check if the settings for the mime type and .pdf extension are correct. Could be that they're linked to a Windows VM, for instance.