When sending a 'mass' email (from a report), The system will automatically change the "TO" address for all emails to that of the signed in user account if the user is sending the email from the TEST site. This is a safety feature to ensure that a blast is not accidentally sent from the TEST site. It also lets you 'test' email tags with real accounts without actually sending the emails to the real people.
The same rule applies when sending individual emails from the Admin of the TEST site.