Make Handling Cost field on the Sales Order Editable

When in a Sales Order with a Customer and Item selected in the Shipping Tab:
Select Shipping Carrier and Shipping Method with Handle Charge enabled.
Notice that the Handling Cost field is not Editable to manually enter an amount.

Alternate Solution:

1. Click the Calculator button beside the Shipping Cost Field
   

OR

1. Click Calculate beside the Shipping Cost in the header of the Sales Order
2. The Handling Cost field now becomes editable even if the shipping cost calculated is 0.00. 
3. Manually enter or change the value in this field
4. Save the Sales Order