After enter a quick reply at the MacNN forums (no text in the entry form, has been entered into the thread) Safari (9A410) still pops up the dialog asking you to confirm closure or quit even though there isn't any new text in the field.
I cannot confirm the bug in Webkit r30368. So WORKSFORME. Jon, feel free to reopen the bug if you still experience the problem.
Yeah, this was probably fixed a long while ago.