A taxpayer whose income tax liability is forgiven pursuant to Section 692 of the Code for any tax year is entitled to a waiver of state income tax for the same tax year, including any related interest and penalty, in the same manner in which the federal tax liability is forgiven. In the case of a joint return, the waiver is equal to the proportion of the tax on the joint return equal to the ratio of the deceased taxpayer's tax liability computed as if both taxpayers were filing separately to the sum of the deceased taxpayer's tax liability and the taxpayer's spouse's tax liability computed as if filing separately.   [PL 2003, c. 287, §1 (NEW); PL 2003, c. 287, §2 (AFF).]