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.

If you want a feedback for Xchat-2 for Windows suggested by Deque (it was the first client I tried), it crashed to me multiple times in a day... moreover it's not mantained since 2009.