add fix if the PO already locked

models/account_move_line.py

@@ -144,10 +144,19 @@ class AccountMoveLine(models.Model):
 
                     # Update PO Line
                     # We update both to ensure consistency
+                    
+                    po = po_line.order_id
+                    was_locked = po.state == 'done'
+                    if was_locked:
+                        po.button_unlock()
+
                     po_line.write({
                         'price_unit': price_unit,
                         'product_qty': product_qty,
                     })
+
+                    if was_locked:
+                        po.button_done()
                         
         return res