For purposes of this subchapter, if a shareholder of an S corporation is both a resident and nonresident of Vermont during any taxable period, the shareholder's pro rata share of the S corporation's income attributable to Vermont and income not attributable to Vermont for the taxable period shall be further prorated between the shareholder's periods of residence and nonresidence during the taxable period, in accordance with the number of days in each period. (Added 1995, No. 169 (Adj. Sess.), § 21, eff. May 15, 1996.)