Cannot re-execute forecast (CBP-consumpt.based planning)

[sap_2605]

Dear SAP experts,

We are assesing forecasting feature in MM-CBP (Consumption Base Planning). When testing I feel odd that I cannot re-execute the forecast in the same period. I have search in SDN and many has proposed to intialize field Initialization in forecasting view. I have followed this advice. After executing the forecast on perion 11, I get the forecast result. And then I change the material master and change the initialization from 'X' (by system) to blank. After that I try to run the forecast again in MP30. In MP30 screen I see that the initialization does show blank. After I click execute, I see that the initialization is set back to 'X' and I got the same error:

The forecast has already been carried out for this period

Msg no PR135

So how to re-execute forecast in the same period?

Best regards,

John

[JL23]

See the logic in  FORM check_wiederholprognose. of ABAP MM61WFAR