And what is the point of banning a user if he can still post in the forum? Don't know if this is the right section to ask this question, if it isn't please move it to the right one.
I think you're seeing posts made prior to the banning. We seldom remove content on MT, so the posts made earlier remain. For example, Skippy's very first post is here; obviously he wasn't banned prior to posting anything -- but the label still reads "banned."