I have a Personal Address Book with my contacts and then 3 Mailing Lists. I've added about 70 new contacts and in the process of double checking that everyone is on the correct mailing lists, found some omissions. If I drag a contact into the mailing list, it creates a new contact in the Personal Address Book with only the display name and email address, but no other contact details. If I double click on the mailing list and type in the name, it again creates a new contact with only the display name and email address and the contact in the mailing list is the new contact. This is only happening with some of the contacts.

Any suggestions?