From our user:

        Samba versions prior to 3.0.8  would  only  support  reading  the
                     fully  qualified username (e.g.: DOMAINser) from the username map

same here:
             When relying upon a external  domain  controller  for  validating
             authentication  requests, smbd will apply the username map to the
             fully qualified username (i.e. DOMAINser) only after the user has
             been successfully authenticated.


Indeed, this comes from the groff file having unescaped backspace characters:

Samba versions prior to 3.0.8 would only support reading the fully qualified username (e.g.: DOMAIN\user) from the

When relying upon a external domain controller for validating authentication requests, smbd will apply the usernam
e map to the fully qualified username (i.e. DOMAIN\user) only after the user has been successfully authenticated.