Here's what this mere mortal found on the IRS web site. Seems to me the excess payment should be treated as a credit against taxes owed and not an additional tax as is currently done.
From 26 CFR Parts 1 & 31.
§31.6402(a)–2 Credit or refund of tax under Federal Insurance Contributions Act or Railroad Retirement Tax Act.
(3) Additional Medicare Tax. (i) If more than the correct amount of Additional Medicare Tax under section 3101(b)(2) or section 3201(a) (as calculated under section 3101(b)(2)), is collected by an employer from an employee and paid to the IRS, the employee may file a claim for refund of the overpayment and receive a refund or credit if the overcollection cannot be corrected under §31.3503–1 and if the employee has not received repayment or reimbursement from the employer in the context of an interest-free adjustment. The claim for refund shall be made on Form 1040, U.S. Individual Income Tax Return, by taking the overcollection into account in claiming a credit against, or refund of, tax.
