Thanks for the response. I have tried what you suggested, but the normal distribution is still not treated as taxable.
Maybe the problem will make more sense if I use some made up numbers:
Lets say the gross distribution (box 1) and taxable amount (box 2a) on my 1099-R are both $1,000. Of that, $500 was rolled over, $300 was a ROTH conversion, and the remaining $200 was a normal distribution. TurboTax allows me to designate the rollover and ROTH amounts. TurboTax says it will assume the $200 is taxable because is it neither a rollover or ROTH, but it doesn't do that. It only shows the $300 ROTH as taxable.
When manually filling out the 1099-R, the "Refund Amount" changes as soon as I click the IRA/SEP/SIMPLE box. Once that is done, the total $1,000 gross distribution is treated as not-taxable. After filling out the 1099-R, Turbo Tax will continue to treat it as non-taxable even if I click on the box that says I "did something else with it (cashed out, etc.)". At that point all of it should be taxable. Any amount I designate as a ROTH conversion will be treated as taxable, but only that amount will be taxable.
I have tried importing the 1099-R, entering the amounts on one form, and as two 1099-R forms (per the TurboTax pop-up and DavidD66's advice). I have not overridden any entries. To see if maybe I have a corrupted file, I have deleted the 1099-R, saved the TurboTax file, rebooted, and tried again. Still the same problem.
