I've noticed that if you go into the content tree and hit publish on an already published comment node it will re-send the notification email to any subscribers. Note that it does not seem to send the admin notification email as well in this case.

It's no biggy but I can't think why you'd want to send the same notification email again so maybe something can be done to stop it.

I cannot see it being too much of a problem unless as an admin I decide to quickly comment from the website UI and then later log into Umbraco in order to tick the 'Is Author Comment' checkbox and hit publish.