MM Contract with Service Entry Sheet

1. I have created WK contract (ME31K), for service (AcctAssgntCategory=K Cost Center, Item Categ=D Service) (100 AU/10 u20AC)

2. Then, I have created purchase order (ME21N) with reference to my contract (100AU/10u20AC)

3. ME81N, Service Entry Sheet and FINAL acceptance for 80AU/10u20AC.

4. MIRO, Post the invoice for 80AU

5. ME22N, Set tik for Final Invoice

6. ME32K Consumption on item level or header level it shows (Wrongly!) that I have counsumed all 100AU

7. I can not make new purchase order for the rest of unused contract (20AU), becouse system assumes all contract has been used.

I have looked for SAP notes, and nothing. Is there some workarond with using tollerance.

Thank you in advance

Best regards