Nonliability for overpayments on government bills of lading or transportation requests.

Notwithstanding the provisions of §§ 47-112 , 47-120 , and 47-121 , or any other act to the contrary, neither the Disbursing Officer of the District of Columbia nor the Auditor of the District of Columbia or any employee in his office authorized by him to certify vouchers, pursuant to the provisions of §§ 47-112 , 47-120 , and 47-121 , shall be held liable for overpayments made for transportation furnished on government bills of lading or transportation requests when said overpayments are due to the use of improper transportation rates, classifications, or the failure to deduct the proper amount under land grant laws or equalization and other agreements.