Problem with ADC

When I added the Active Directory Connector to the w2k DC (also Global Catalog) it seemed to go through the AD and “match” the mailboxes fine. But then I noticed that a couple (15 out of 700) mailboxes were actually turned into Custom Recipients with no Primary NT account associated with them. I spoke with a friend that had performed a migration and they said that the same exact thing had happened. Has this happened to anyone else and does anyone know why it happened. I spoke with Microsoft Tech support and they couldn’t figure it out and told me to restore the mailboxes from backup. Thanks in advance.