It has always been like this. But it is technically new, as it's the first time it's been seen as a finalized post. I think it would be more inconsistent to not show a new button on it (given that everything else above it would have it).
But is consistency more than "what is right"? I think labelling it as new makes the user feel as though the post is unread and contains new content, but it doesn't have new content if I have posted it.