The SSL system always makes pages which show up with a browser warning such as "contains insecure items."
This is because the media_url is based on the settings.MEDIA_URL. If that points to an http:// address, then all pages will use http:// addresses for media content.
To fix this in the cleanest manner, the media_url in the page context should understand what to do in a secure context.
Reported by bkroeze