With respect to:
the general assembly covenants with the bureau and the purchasers or owners of the bonds or other obligations described in this section that this chapter will not be repealed or amended in any manner that will adversely affect the collection of the tax imposed under this chapter or the money deposited in the promotion fund or the alternate revenue fund as long as the principal of or interest on any bonds, or the lease rentals due under any lease, are unpaid.
IC 6-9-2-4.9