Cannot edit line on purchase order

Question

I cannot edit a line on a purchase order (no fields can be editted). I checked linked documents and found that the line had been copied to an AP invoice partially - the line on the PO is still open with an open amount.
Why can it not be edited now?
To reproduce:
Create PO (service type)
Enter description, GL account, price. $500
Add
Copy to > AP invoice
Change amount to $250
Add
Now the line on the PO cannot be edited. Status of line is open and open amount $250.
I want to edit the line total but cannot.

Answer 1

Hi Maeve Cahillane ,
As Gordan said its a system design. But u want to post remaining amount u can do, as the PO is still open  so u can give copy to to Ap invoice.
Regards:
Balaji.S