As far as I know there is no "in between" way of doing this... you either have all your accounts with the Samba/POSIX attributes, or none.
My guess is that the admin account (and possibly all accounts created before you preformed the samba extensions install) doesn't have the samba object class installed. So when the LDAP extensions defined in the samba admin extension try to set the Samba attributes they fail as they are not allowed on that account.
If my guess is correct the output of the following command will be missing either one or both of the samba / posix objectClass'
Code:
zimbra@email:~$ zmprov ga admin@domain.com | grep objectClass
objectClass: organizationalPerson
objectClass: zimbraAccount
objectClass: amavisAccount
objectClass: posixAccount
objectClass: sambaSamAccount
To add the correct objectClass'es to existing accounts you need to run the commands found at the end of the linked section here:
UNIX and Windows Accounts in Zimbra LDAP and Zimbra Admin UI 6.0 - Zimbra :: Wiki
Hmmm... there might be a way to actually do this without adding those attributes if you are set against it. You could try disabling the admin extensions and changing the password, but be warned that all accounts with those objectClass extensions will probably not show up, or other crazy behavior...