I've noticed that deleting a member from the Security section of the CMS doesn't actually delete a member, it just delete's the record for that member in Group_Members.
Why is this? Especially when Silverstripe's own unique member identifyer is an email address? Even when you delete a member, a member can't re-register using the same email as it's still in the system despite being "Deleted"
My other question is: Does anyone know how I can fix this?