Have you clicked the Continue button on the page that lists the Forms 1099-R that you have entered and entered your year-end value in traditional IRAs (or entered it directly on line 18 of the IRA Information Worksheet)? It appears that TurboTax limits your carryover basis to an amount no greater than your year-end value in traditional IRAs, although I don't think that that limitation is appropriate and is a bug in TurboTax. I reported this bug (and a related bug involving HFDs) more than 5 years ago and have not seen any evidence that this bug has been addressed.
