I noticed the behaviour exposing your SessID in other Simple Machines Forum. Maybe could be another issue.
Furthermore i can confirm Firefox establishes a partial encrypted connection to
https://evilzone.org as displayed in website's informations.
EDIT:
And guess what? Editing this post being in https, I got a popup saying the data would have been sent in clear text, and after having saved the post I have no more https in my url bar, just evilzone.org/........
@proxx, didn't pay attention you already mentioned this... i get exactly the same message you posted. However it's an additional confirmation.