usermod -G

Greetings,

SPARC box running Solaris 10.

bash-3.2# cat /etc/release
                       Solaris 10 10/09 s10s_u8wos_08a SPARC
            Copyright 2009 Sun Microsystems, Inc.  All Rights Reserved.
                         Use is subject to license terms.
                            Assembled 16 September 2009

                   Solaris 10 8/11 (Update 10) Patchset applied.

`usermod -G` complains about the group name being too long:

bash-3.2# usermod -G abcd,abcdefgh1034,abcdef103 user852
UX: usermod: user852 is currently logged in, some changes may not take 
effect until next login.
UX: usermod: abcdefgh1034 name too long.
UX: usermod: abcdef103 name too long.

(I guess, because the group name is longer than 8 characters), but adds 
the user to the additional groups:

bash-3.2# cat /etc/group | grep user852
abcd::100:user852
abcdefgh1034::102:user852
abcdef103::103:user852

However, If I add the user to the first secondary group, like `usermod 
-G abcd user852` then latter I add the same user to the second secondary 
group, like `usermod -G abcdefgh1034 user852`, `usermod` removes the 
user from the first secondary group.

Any explanation for this (miss)behavior, or I am doing something wrong.

Regards,

Ioan