IDOC to IDOCstring not doing EDI_DC40 seg name

Dear All I am using the service pub.sap.idoc:encodeString in Integration server version 8 and it mostly is ok apart from the fact that the EDI_DC40 record name is being missed. Can anyone throw some light on this? Many thanks

      1000000471108150000    502   FINSTA01                      FINSTA01                      FINSTA                               D96A  FINSTATEST_RFC B   TESTFII2                       111284667696805                                                        SAPXXX    LS  GB00                           1110131001234                                                         2010031900000110078                                                                                                                               

E1IDKU1 100000047110815000000000100000001REM 10078 9RG