(a) Any proceeds of the sale of bonds issued under this subchapter that are unspent after completion of the project for which the bonds were issued:
(1) shall be deposited to the credit of the bond and interest redemption fund for the bonds; and
(2) may be used only to:
(A) pay the principal of the bonds; or
(B) purchase outstanding bonds of the issue from which the proceeds were derived.
(b) A bond may not be purchased under Subsection (a)(2)(B) for a price that exceeds, excluding accrued interest, the face amount of the bond.
(c) A bond purchased under Subsection (a)(2)(B) must be canceled and may not be reissued.