Unfortunately this problem (or something similar) still persists in the online version. If you take distributions from both an inherited IRA with no basis, and a regular IRA with a basis, then they both get blended together in worksheet 1-1.
Workaround: When asked for 'Total 12/31/20 value of all your "Traditional IRAs"', as long as you *exclude* inherited IRAs from your response, the inherited IRA won't screw up the cost-basis and you'll (apparently, based on a review of the 8606) get the right result.
