No carryforward and no carryback arising for a taxable year for which a corporation is not an Alabama S corporation may be carried to a taxable year which such corporation is an Alabama S corporation. No carryforward and no carryback shall arise at the corporate level for a taxable year for which a corporation is an Alabama S corporation. Nothing in this section shall prevent treating a taxable year for which a corporation is an Alabama S corporation as a taxable year for purposes of determining the number of taxable years to which an item may be carried back or carried forward.