External forecast uploaded on weekly bucket ignored when first day of the week is off period

Summary:

External forecasts are uploaded on weekly basis. They are ignored when the first day of the week is off period.

Content (required):

Our customer uploads external forecasts to Supply Planning on a weekly basis.

Therefore, the date that they use for the import in the FBDI is the first day of the week which is Monday.

However, if this day is set as an non-working day exception, then the forecast is simply ignored for the rest of the week.

Is it a standard behaviour? What should be the correct way to do in this case?

To be complete, the supply plan is contrained.