After submitting a first top-level comment, the Submit Comment and Preview buttons would stop working. Fix this by inserting a new blank comment preview element before deleting the old one.
Once that was fixed, trying to submit a blank comment produced an error message, which would persist even after successfully submitting a non-blank comment. Fix that by hiding the error element on a successful submission.
After submitting a first top-level comment, the Submit Comment and Preview buttons would stop working. Fix this by inserting a new blank comment preview element before deleting the old one.
Once that was fixed, trying to submit a blank comment produced an error message, which would persist even after successfully submitting a non-blank comment. Fix that by hiding the error element on a successful submission.