IWP : PDF downloads over HTTPS fail in IE7

[xochi]

I have a PDF stored in a container field (the whole file is stored, not a reference). I'm trying to load the file via IWP with the following results:

Mac Safari : works

Mac Firefox : works

Win XP Safari : works

Win XP Firefox : works

Win IE 7 : Fails

When IE7 fails it displays

"IE Cannot download data.file from data.mydomain.com. IE was not able to open the internet site. The requested site is either unavailable or cannot be found. Please try again later".

It turns out if I run IWP over http:// rather than https:// it works on all browsers.

Why is IE the odd-man out here?

IE 7.0.5730.11 is the version I'm using, with XP Home SP2 + all recent updates.

Is anyone out there running IWP over HTTPS and able to test a PDF download?