Comment Moderation Notification Issue

Under Settings > General > E-mail Address (“This address is used for admin purposes, like new user notification.”) I have specified an email address (webmaster@MYDOMAIN), which is not a registered with my blog and which is different from any of the email addresses used by blog administrators. Yet, when I get a comment that needs to be approved I get a notification message to the webmaster email address and to administrator email address. Why is this? I would like new comment notification and moderation notices to go only to the webmaster address. Deactivating all plugins makes no difference.