Any coupons for the payment of interest on the bonds shall be considered for all purposes as warrants drawn upon the current expense fund of the county issuing bonds, and if when presented to the treasurer of the county no funds are in the treasury to pay them, the treasurer shall indorse the coupons as presented for payment, in the same manner as county warrants are indorsed, and thereafter they shall bear interest at the same rate as county warrants presented and unpaid. If there are no funds in the treasury to make payment on a bond not having coupons, the interest payment shall continue bearing interest at the bond rate until it is paid, unless otherwise provided in the proceedings authorizing the sale of the bonds.