After change delivery date(VBEP-EDATU) via BAPI_SALESORDER_CHANGE, schedule line split into 2 items

Hi experts.

I created MTO sales order and changed its delivery date via BAPI_SALESORDER_CHANGE.

It has 1 schedule line item confirmed quantity filled but after BAPI, it split into 2 items.

One has old delivery date, zero order qty, zero rounded qty and filled confirmed qty.

The other has changed delivery date, filled order qty, filled order qty and zero confirmed qty.

Why it split (or not changed confirmed qty) and what settings do I need to check?

Thanks in advance.