Mixed-content shield won't allow "Enable protection"
On an HTTPS web page with mixed content (!https://us.travelctm.com/), I see the usual alert icon and a little broken shield that seems to offer the ability to block non-HTTPS resources. However, when I click "Enable protection" under "Options", the page reloads, but the shield remains broken, the message is still "Protection is disabled", and "Enable protection" still appears under "Options".
This is with 5.0a3. HTTPS Everywhere says that the only rules active are "Twitter.com" and "Google APIs".