I don't think the empty subject line is directly related. Or at least, I have never experienced it. It looks like you can reproduce it. Your post has no subject line. How did you do that? The odd thing is, I can not reply to your post unless I add a subject line. Is this a browser issue?
Edit: I experienced the problem. The subject line vanished when I tried to edit the post. But I couldn't submit it, saying empty subject is not allowed.
Looking again at the original topic, the new in-line editing feature, I think it is a step back. People want to march the old web forum towards instant messaging.