Thanks!
I deleted his 1099R for the inherited IRA withdrawal, and re-entered it to ensure that it is correctly marked as an inherited IRA, which it appears to be. I believe that an inherited IRA can have a basis if the original owner made nondeductible contributions; in our case, there were no nondeductible contributions, so no basis.
I spent two hours on the phone with TT support, including with their Tax Advice group, and no resolution. They need to do more research!
Even IRS 590-B for 2019 (no 2020 yet available) says you cannot use one 8606 for two withdrawals, both of which have a basis. You have to use two 8606s. I am still hopeful it's a TT bug.
Thanks again for your help and quick response.
