This is the expected behavior. When you have basis in nondeductible traditional IRAs, until you enter the year-end balance in traditional IRAs, TurboTax is unable to calculate the correct taxable amount of the distribution on From 8606 Part I because the calculation initially assumes that the year-end balance is zero. Once you enter the year-end balance, TurboTax corrects the calculation and comes up with the correct, higher taxable amount.
