Sec. 4. (a) A taxpayer who is subject to taxation under this article for a taxable year or part of a taxable year is not, for that taxable year or part of a taxable year, subject to the income taxes imposed by IC 6-3.
(b) The exemption provided for the taxes listed in subsection (a) does not apply to a taxpayer to the extent the taxpayer is acting in a fiduciary capacity.