In computing the lump-sum payments made to Air Force reserve officers under the provisions of [section 2 of the Act of June 16, 1936], as amended and to reserve officers of the Navy or to their beneficiaries under [section 12 of the Act of August 4, 1942], as amended, no credit shall be allowed for any period of active service performed from June 24, 1948, to the date on which this chapter shall cease to be effective. Each such lumpsum payment shall be prorated for a fractional part of a year of active service in the case of any reserve officer subject to the provisions of either such section, if such reserve officer performs continuous active service for one or more years (inclusive of such service performed during the period in which this chapter is effective) and such active service includes a fractional part of a year immediately prior to June 24, 1948, or immediately following the date on which this chapter shall cease to be effective, or both.