did you ever get a good answer for this? Having same problem this year. Made contributions and conversions for two tax years in 2017 (i.e., for 2016 and 2017). 1099-R amount covers both conversions, but turbo tax questions only get at tax basis as of 12/31/16 (0), 12/31/17 (0), and 2017 tax year contributions made in 2017 or through April 2018. There is apparently no place to indicate that 2016 nondeductible contributions were also made in 2017 that would create basis for the 1099-R amount to be fully non-taxable, and putting a higher amount (covering both tax years) for 2017 contributions leads to Turbo tax incorrectly identifying them as excess contributions, subject to a penalty tax.
