I have tried fixing this manually under the AMT section by selecting "I need to make an AMT adjustment to my investment income or expenses"
I put the (negative) difference in AMT versus non-AMT cost basis under the question: "Enter any AMT adjustments you need to make to your investment income. You can enter positive or negative numbers." "Gross investment income".
This option appears to have no effect, and regardless of what is entered, it doesn't change what TurboTax lists as "Alternative minimum taxable income."
