By the way, is the subject field really necessary? It is a 'quick' reply right? I don't think anyone would bother changing the subject in a quick reply. Just asked anyway.
I have to agree with AliasM2K. I would also leave the subject line away. In case someone wants to change the subject (Why would someone anyway, when he is replying to the topic?), he or she could do that in the full editor. Nevertheless, like the fact that the quick reply shows now without having to click another button.