No what I meant was the quantity being passed may not be considered.
I just checked documentation of the BAPI, it says:
Delivery quantities (STOCK_TRANS_ITEMS-LFIMG)
If no delivery quantities are specified, the delivery creation date is used to determine the delivery quantities from the schedule lines. Otherwise, the delivery quantity is copied from the original quantity.
If the delivery quantity is specified, the sales unit must be specified, either as an SAP code (SALES_UNIT) or an ISO code (SALES_UNIT_ISO).
Delivery quantities can only be specified for individual order items.
can you post you structure population code snippet