Thanks. This does in fact seem to be fixing the issue. It seems that TurboTax, though it knew all of this information because I imported my 2016 TurboTax return, did not do the right thing. I needed to explicitly say I had nondeductible contributions (TurboTax encourages you to say no) and add that basis.
@macuser_22 if you mark this as an answer rather than a comment I'll mark it as the answer.
