MyBB Community Forums

Why is it that when a member posts a message in a forum and I go to look at it when I go back to the main board the forum still shows the icon for "Forum Contains New Posts" rather than the icon for "Forum contains no new posts"

Surely as I have read that one it should mark the board as read?

Is this a bug or a strange feature that I'll have to hit the mark all forums read button?

Thanks!