MHTML on HTTPS with IE7

When using MHTML over https in IE7, IE7 shows the non-secure items popup. I believe this is due to the mhtml: prefix. IS this 开发者_Python百科actually a bug? or is there a workaround for it?

Starting here is a good thread kind of explaining some options. We just ended up not supporting IE7 since it's only a couple percent of our users now anyway. http://www.phpied.com/mhtml-when-you-need-data-uris-in-ie7-and-under/#comment-72154