(1) Notwithstanding any other provision of this Act, where:
(a) throughout any part (in this subsection referred to as the relevant part ) of the prescribed period, a prescribed member held an acting or temporary rank; and
(b) the amount paid by, or deducted from the pay of, the member in respect of a contribution payable by him during the relevant part of the prescribed period was less than the amount of that contribution but was equal to the amount that would have been the amount of that contribution if the member had not held that acting or temporary rank;
that member or the personal representative of that member, as the case requires, is not liable to pay the difference between the amount of that contribution and the amount so paid or deducted unless:
(c) the member retired or died at the end of the relevant part of the prescribed period; and
(d) by reason of his retirement or death, a pension benefit, or a deferred benefit applicable under Division 3 of Part IX, became payable during the prescribed period.
(2) In ascertaining, for the purposes of this Act, the amount of a refund of contributions or the amount of a lump sum required to be calculated by reference to contributions, the amount of a contribution a part of which, by virtue of subsection (1), a member, or the personal representative of a member, is not liable to pay shall be taken to be reduced by the amount of that part.
(3) Where:
(a) after the commencement of this section, a prescribed member, or the personal representative of a prescribed member, who, during the prescribed period, held an acting or temporary rank, is liable to pay an amount to the Commonwealth in respect of contributions that were payable by the member when he held that rank by reason that the amounts that were paid, or deducted, in respect of those contributions were calculated by reference to the contributions that would have been payable if the member had not held that rank;
(b) a benefit has become payable to or in respect of that member, being:
(i) invalidity pay payable to a member classified as Class A or Class B under section 30;
(ii) a spouse pension under section 38;
(iii) a child's pension under subsection 42(2) or 43(2); or
(iv) a deferred benefit applicable under Division 3 of Part IX that is of the same nature, and payable in the same circumstances, as a pension referred to in subparagraph (i), (ii) or (iii); and
(c) but for this subsection, the amount of the liability referred to in paragraph (a) would exceed the amount that was payable to or in respect of the member during the prescribed period in respect of benefits referred to in paragraph (b) but was not paid during that period;
the amount of the liability referred to in paragraph (a) is reduced by the excess.