client is Mac OS X 10.3.2 (panther), latest Apple updates applied.
server is SAMBA 3.0.1 on SPARC Solaris 9.

When client connects to share, and gives username manually in uppercase (as if
the client default), then supplementary groups are not picked up. 

logfile:

...
[2004/01/14 12:21:22, 5] auth/auth_util.c:debug_unix_user_token(505)
  UNIX token of user 1298
  Primary group is 1009 and contains 2 supplementary groups
  Group[  0]: 1009
  Group[  1]: 1009
...

If exactly the same share is connected to, but the (same) username is entered in
lowercase the problem goes away thus:

Logfile:

[2004/01/14 12:22:52, 5] auth/auth_util.c:debug_unix_user_token(505)
  UNIX token of user 1298
  Primary group is 1009 and contains 7 supplementary groups
  Group[  0]: 1009
  Group[  1]: 1009
  Group[  2]: 1007
  Group[  3]: 1014
  Group[  4]: 1017
  Group[  5]: 1024
  Group[  6]: 1025

bug only observed using Mac OS X as client, *doesn't* happen with win2k clients.
Server is using LDAP to retreive uid's/gid's via nsswitch (Sun 'ldap' nss
backend).  LDAP NSS backend is independent of SAMBA.  Bug is reproducible with
different usernames.

SAMBA configure options:
--without-krb5 \
--without-included-popt \
--without-acl-support \
--without-libsmbclient \
--without-pam \
--without-ads \
--without-ldap \
--without-winbind