(1) When, by mistake or error of the treasurer, county clerk and recorder, or assessor or from double assessment, a tax lien has been sold on land upon which no tax was due at the time, the county shall reimburse the purchaser in the amount paid by him in connection with the purchase of the tax lien on such land, together with interest from the date of purchase at the rate which is determined as provided in this section. Reimbursement shall be made from the various funds to which the tax was originally distributed; except that interest shall be paid from the county general fund. The treasurer, county clerk and recorder, or assessor, as the case may be, and his sureties on his official bond shall be liable to the county for such amounts reimbursed as a result of sales made only through willful misconduct.

(2)

(a) The annual rate of interest shall be two percentage points above the discount rate, which discount rate shall be the rate of interest a commercial bank pays to the federal reserve bank of Kansas City using a government bond or other eligible paper as security, and shall be rounded to the nearest full percent.

(b) Notwithstanding any other provision of this subsection (2), the rate of interest shall be no lower than eight percent per annum compounded annually.

(3) The commissioner of banking shall establish the annual rate of interest based upon the computation specified in subsection (2) of this section. Such annual rate of interest shall be so established as of September 1, 1981, to become effective October 1, 1981. Thereafter, on September 1 of each year, the annual rate of interest shall be established in the same manner, to become effective on October 1 of the same year.