OK... by tweaking the numbers by $1, I could see how each field affected the result.
ABP adjustment is (1099-INT Box 12) + ((1099-OID Box 6) * 1099-OID Box 8)/(1099-OID Box 8 + 1099-OID Box 11)
1099-OID Box 10 could also be in the equation, but mine is empty.
Basically, TurboTax is adding the Treasury bond premium to the OID acquisition premium X the % of taxable OID income to total OID income. I believe it's doing this since1099-OID Box 6 could contain acquisition premium of both taxable and non-taxable bonds.
The solution is to split the OID into 2 copies, one for taxable and one for non-taxable income. (This is the same problem/solution when adjusting for accrued interest when the 1099-INT contains both kinds of income.)
