Constrained MRP Plan: "Firm Components" feature in Supplies and Demand is not working as expected

Summary:

The "Firm Components" feature in Supplies and Demand is not pegging the revised component to the FG(Assembled Item) planned order.

Content (required):

I am using the Firm Components feature on the Planned order for an assembled item. The planned order is pegged to component A and using this feature I want the Planned order to be pegged with component B. Once this planned order is released, I am expecting the work order to show component B.

In this case, neither the planned order gets pegged with component B nor it is visible on the work order. Anyways if the planned order is not pegged with component B in supplies and demand, Component B is not going to flow to the work order too.