Refunding obligations issued as provided in section 4154 may be sold or exchanged for outstanding obligations issued under this chapter and, if sold, the proceeds from them may be applied, in addition to any other authorized purposes, to the purchase, redemption or payment of those outstanding obligations. Pending the application of the proceeds of any refunding obligations, with any other available funds, to the payment of the principal, accrued interest and any redemption premium on the obligations being refunded, and, if so provided or permitted in the resolution authorizing the issuance of these refunding obligations or in the trust agreement securing them, to the payment of any interest on refunding obligations to be refunded or the trust agreement securing and any expenses in connection with refunding, such proceeds may be invested as specified in the resolution authorizing the obligations and any expenses in connection with refunding, such proceeds may be invested as specified in the resolution authorizing the obligations to be refunded or the trust agreement securing them. These investments shall mature or shall be subject to redemption by their holders, at the option of the holders, not later than the respective dates when the proceeds, together with the interest accruing on them, will be required for the purposes intended.   [PL 1987, c. 141, Pt. A, §6 (NEW).]