Cannot reschedule without creating a planning order for more than the quantity of the sales order

Summary:

I am testing an operation to change the scheduled ship date via SP for an order that has failed to reserve inventory since out of stock.
For an order with a scheduled ship date of 11/29 and an order quantity of 4000, I manually created a planned order for 4000 units on 10/7.
When I linked this to GOP and rescheduled the order, I expected that the scheduled ship date of the order would change to 10/7, but the result was that the scheduled ship date did not change.
Do you know what is causing this?

However, if the quantity is made more than 4000, the scheduled ship date of the order will change after rescheduling.