It seems FreeTaxUSA has a BUG when entering two 1099-B from two banks, which both contain adjustment, such as "F. accrued market discount".
1) Enter the first 1099-B with adjustment F. In Preview - Schedule D / 8949, 1b and 8b are filled correctly.
2) Then, enter the second 1099-B, which also contain adjustment F. The error appears! In Preview - Schedule D / 8949, 1a and 8a are filled for the second 1099-B.
The correct action should be the second 1099-B figures are added to Schedule D, 1b and 8b.
Also, does anyone know how to edit Schedule D / 8949 directly in this software? If so, I could bypass this error and correct Schedule D / 8949.