Aha! For some time now, I have had problems with Opera and forums. Opera does not remember my logins, and also forgets all my settings I do on sites (cookie controlled settings).
Opera have been more or less unusable on many sites because of this. I was forced back to IE on several sites.
I never suspected Spybot caused this behaviour!
I will try to unprotect Opera cookies in Spybot and see if that helps.
Thank you ketas for bringing this up.