BAPI_PO_CHANGE for Service Items

I am using BAPI_PO_CHANGE to change a Service Order. In this scenario I am changing the quantity. I am running the FM just with the PO number no other data. I get the following messages at the end: I                      000 Function "Change Purchase Order" Performed in Test Run S 06                  022 No data changed I checked OSS Note 1382965 but this seems to point to the Account Assignment Has anybody managed to get over this sort of behaviour? Many thanks, EB