Why the Cost Center field in a Requisition line item is set back to blank when the Account Assignment is Order (F)?

If you want the system to respect the value provided in cost center field on a requisition for account assignment order, the parameter Application.Common.EnableCostCenterFieldIfAccountAssignmentIsF(Order) should be enabled.

Even if you configured the values correctly in AccountCategories.csv file, it is mandatory to have this parameter enabled if you want to use cost center on a requisition line item with account assignment Order (F).

For more details on Account Categories configuration, please refer How do I make an accounting field visible and required for all account categories?

Core Procurement > Core Administration > Core Accounting
Purchasing > Requisition/Order Accounting