Maryland Code, Local Government § 20-118

(b)(1) Except as provided in paragraph (2) of this subsection, if a claim for refund is allowed, the tax collector shall pay interest on the refund at the rate set under § 13-604(a) of the Tax--General Article from the date on which the tax, fee, charge, interest, or penalty was paid to the date the refund is paid.

(2) A tax collector may not pay interest on a refund if the claim for refund is based on an error or mistake of the claimant not attributable to the county or municipality.