samba - Mar 2013 - smbldap-groupshow shows group, /smbldap-groupmod says "group X not found"

Hi,

running an old Samba version 3.x I have issues with a few groups. One
example is:

$ getent group | grep 3PL
3PL-:x:1054:$lotsofusers
$ /usr/sbin/smbldap-groupshow 3PL
dn: cn=3PL,ou=Groups,o=company
objectClass: posixGroup,sambaGroupMapping
cn: 3PL
gidNumber: 1054
sambaSID: S-1-5-21-1373160827-2058509255-2139411751-3109
sambaGroupType: 2
displayName: 3PL
memberUid: $lotsofusers
$ ldapsearch -x objectclass=sambagroupmapping | grep 3PL
# 3PL, Groups, company
dn: cn=3PL,ou=Groups,o=company
cn: 3PL
displayName: 3PL
$

*But*:

$ /usr/sbin/smbldap-groupmod -m $newuser 3PL
/usr/sbin/smbldap-groupmod: group 3PL not found!
$

What's wrong here? And how can I fix it (if)?

Thanks, Helmut