According to RFC 4120 5.4.1:

   KDC-REQ-BODY ::= SEQUENCE {
        kdc-options [0] KDCOptions,
        cname [1] PrincipalName OPTIONAL
                                    -- Used only in AS-REQ --,
        ....

However, we do fill in the cname field for TGS-REQ. Should remove that field.