Get your taxes done using TurboTax

My issue is pretty simple.  I'm trying to see how my capital gains rate is 0%.  My wife and I are well below the taxable income of $80,000 (more like 36,000).  We had $14,003 in long term capital gains.  TurboTax figured our tax to be $1796.  Then I went back and changed the basis of our stock sales to render a zero ($0.00) long term capital gain, to see what would happen.  I changed nothing else.  With this the only change, TT figured our tax to be $613.  Taxable income was significantly lower.  How can this be, if we are supposed to be paying 0% on capital gains?  Is TurboTax wrong?