This may be a small bug.
We entered a subscriber's email address and first name (The subscriber was added thru the settings subscriber screen). After some testing we deleted the subscriber.
We then keyed in the same subscriber's email address thru the subscriber box on our website.
When checking the subscriber list that subscriber is back displaying the first name. There is no way to enter the first name thru the subscriber box on the website which leads me to believe that record was never really deleted.