It appears that TurboTax fails to ask you to provide the required explanation statement when you indicate a traditional IRA contribution and follow that up with indicating that you had some or all of it returned, instead asking for explanation when you enter a Form 1099-R that indicates the return of contribution. If the return of contribution is made in the year following the year for which the contribution was made, TurboTax developers apparently assumed that you would file reporting the excess contribution and then amend when you receive the Form 1099-R for the return of contribution. You can either prepare such a statement manually and include it with your mailed tax return or you can try creating a dummy Form 1099-R with zeros in boxes 1 and 2a, code 8 in box 7 and the IRA/SEP/SIMPLE box marked. This will trigger TurboTax to prompt you to enter and explanation after you click the Continue button on the page that lists your Form 1099-R entries.
