that's because a secure connection cannot be established, when you add the "s" the connection gracefully fails because TLS renegotiation fails. It leaves the "s", but isn't secure. This is why any post or log in attempt you make while on https fails.
You can see this best in Opera, for a moment it'll switch to a secure connection before it's dropped when renegotiation fails.
It'll probably never be fixed. After all "it's just a gaming forum"