Work Order scheduled dates - User Scheduling - Schedule Firm

Summary:

The work order start and end dates are not getting saved as per user input even with the User / External Scheduling and Schedule Firm

Content (please ensure you mask any confidential information):

I started to create a work order with scheduled date of tomorrow and created an operation as well. I have selected user/external scheduling as well as Schedule firm options and saved the WO. Now, I changed the end date to 17th Sep, retaining the start date as tomorrow and expect the system to retain these dates. However, the work order's start date as well as operation's start and end dates are also now updated to 17th Sep, making all the dates equal to 17th Sep, which I don't want. I would like to plan the WO date as 16th to