20. The payment of the pension credit of a pensioner who elected to be a member of the plan pursuant to the first paragraph of section 18 ceases to be made for the period during which the pensioner is a member of the plan, and the second paragraph of that section applies with the necessary modifications in respect of any amount of pension credit which must be remitted to Retraite Québec. The pension credit becomes payable again on the day that follows the day on which the pensioner ceases to be a member of the plan, and the actuarial reduction that applied thereto, where applicable, is recomputed in accordance with the second paragraph of section 19, with the necessary modifications.