Open Item Field in Purchase Requisition is not zero after Schedule Agreemen

Hi Experts,

I have created a Purchase Requisition with open item 10 amount 20. When I create with Purchase Order in reference with Purchase Requisition, it will make the open item qty in that PR zero. But when create Scheduling Agreement referencing Purchase Requisition, it will not make the open item qty of PR zero. Why? Is this a standard functionality? And How can I make the open item qty zero on the referenced PR creating a Scheduling Agreement? Are there configuration for this requirement?

Thanks for your answers.