Production Order Header - Committed Quantity

Hi Team,

I have created the production order with quantity 2. In order to produce the 2 header item, i need to 2 components (BOM item). But currently i have only 1 quantity of  BOM item in stock. With this condition, i am performing the ATP check in my production order. Since i have only one BOM item in stock, i can able to produce only one header item. So after executing ATP check in my production order, i am expecting the below field to be updated as "ONE" (refer the screen shot). But it is not getting updated. Why? When this field will be updated?

Thanks