Retirement tax questions

I'm using Turbotax Premier and I converted my IRA to a Roth--I do this every year.  I put money in an IRA.  Then immediately convert it to a Roth IRA.  So there's no taxable income.  Everything is going fine, turbo tax even says I won't have to pay taxes on this distribution.  But my Federal tax due reflects a payment due.  I feel this must be a bug in Turbo tax this year (I've never had this problem before).  Any clues?