Manually loaded firmed planned orders as collected data in ASCP expiring forecast in a ECC Plan

I am loading firmed planned orders as collected data in ASCP using supply staging table MSC_ST_SUPPLIES. As per Oracle user guide, I will need to associate the planned orders with a schedule designator (MPS) and this schedule designator needs to be in the plan options as demand schedule for the organizations that I am loading. When I do that, its expiring the demand beyond the last planned order associated with the schedule designator. In other words, its considering demand only within the horizon of the schedule designator. Any pointers on how I can prevent demand expiration?