By default, SDT is designed to instanciate in its own private DS so its meta data tables are protected. I would add 1 additional line to see if that resolves your problem:

IF THIS.OpenDefaultDatabase()
   IF THIS.PARENT.oMeta.SetDatabase(DBC())
      IF THIS.PARENT.oMeta.oSDTMgr.NeedUpdate()
         THIS.PARENT.oMeta.oSDTMgr.UPDATE()
      ENDIF
   ENDIF
   && THIS.CloseDefaultDatabase() && why is this needed???
ENDIF

I would also look through the code in the OpenDefaultDatabase method to see if the SetDatabase method in SDT is being called. Also, keep in mind that I am not using MM, so I am speculating what you rally need to do, but the SETDATABASE method call establishes in SDT what DBC to use.