Form action on tweakers.net does not get rewritten
On gathering.tweakers.net (forum), registered users can reply to topics. When you hit the button to see either a preview or actually post the message, Firefox (I think Chrome didn't, but don't know if that means it just kept quiet or rewrote the link) will complain saying "The information you have entered on this page will be sent over an insecure connection". Example:
Yes, they use absolute http-URLs everywhere.