For mostly historic reasons our default DNS domain (lets call it new.example.net) differs from our Kerberos REALM (OLD.EXAMPLE.COM)
Actually the KDC (an Active Directory Server) does not know about this newer domain at all.
In Linux clients this seems to get a problem when trying to access a source on "server1.new.example.net".
The client will try to request a Service principle of the following form: cifs/server1.new.example.net@OLD.EXAMPLE.COM
This will not work as valid servicePrincipalNames would only be: cifs/server1@OLD.EXAMPLE.COM and cifs/server1.old.example.com@OLD.EXAMPLE.COM
Unfortunately I did not find an option for krb5.com to do some domain mapping for servicePrincipalNames to enforce a FQDN of "old.example.com" in any case.