very strange problem on aix-based system

Hi all.
I'm debugging a system (AIX 4.3.2 ) delivered to the government for
which I have no way to contact the original software developers. The
problem I'm trying to fix is that when a user logs on to the system
they are instantly switched to being the administrator. The user
accounts are created with some custom software, but after that a user
account looks like a normal account created using smit. The user
accounts have a primary group of... let's call it "xx_user." The
administrator account has the group set to "xx_admin," which is also
the login name. When I log on as a user (i.e., joe_user) and open a
dtterm window and do whoami, it says I am "xx_admin." When I look at
the standard AIX audit trail I see the joe_user login, but after that
all activity is shown as xx_admin. However, when I create a user
account using smit and assign it to the developer group, "xx_dev," this
problem does not occur. I've done a grep on all the source code and
can't find anything that looks suspicious. Right now I'm completely
stumped and would welcome any suggestions. Thanks.

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