So this is a bit complicated. The discussion was merged from a temporary one and existing one. So far so good. Then installed the "Change post author and date" extension and changed my reply at the end to be on top of the thread (date earlier then the 1st post).
Since then I can see all new replies but on the front page the discussion is always marked as read, even though it moves up in the list.
How can this be fixed? Change in DB or what is triggering the unread class?