Posting Exchange Rate Diff to another GL than expenses GL

Dear Experts ,

1. I have maintained the "KDM" in OBYC

2. I have maintained the Exchange rate diff treatment to be blank in OMRW

3. I have created a PO ( against PM Order ) , then I have done the GR , then I have changed the exchange rate , then when I simulate MIRO , the difference is posted to the Expenses account ( PM Order ) , not the KDM account , could you please advice

Note : I understand that KDM is  triggered if the material cannot be debited or credited due to standard price control or lack of stock.

so what is the solution to make the posting happen to KDM Account ??????

Thanks in advance for your help