HP has confirmed the change from 10.x to 11.x in the setting of the
group id at login time vis-a-vis /etc/logingroup.

It's not documented, but now the behavior is sort of the *reverse* of
10.x behavior:

10.x:
  o no /etc/logingroup --> only GID is that from /etc/passwd.
                  The user must execute 'newgrp' to change GID.
  o /etc/logingroup exists --> user is effectively the member of every
                  group in which he is listed in /etc/logingroup, without
                  having to do a 'newgrp'.

A common trick is simply 'ln -s /etc/group /etc/logingroup' if you want
membership in all groups listed in /etc/group.

11.x:
  o no /etc/logingroup --> user is effectively the member of *every*
                  group in which he is listed in /etc/group
  o /etc/logingroup exists --> user is effectively the member of *only*
                  the groups in which he is listed in /etc/logingroup.

So, the "workaround" to get 11.x to behave as 10.x did, is simply:

  # >/etc/logingroup

Now the user is now not listed in any groups in /etc/logingroup and so is
only a member of the group listed /etc/passwd. I'm not sure why you'd ever
want to fall back to the 10.X behavior except, maybe, legacy situations of
some sort.