I think I've discovered a workaround for this bug. On the Form 1099-OID for the brokerage(s) in question, scroll down to the "Adjustments to OID Interest" section and check Box H - Other. Then enter the Box 10 amount of OID bond premium as a positive value (it will be treated as a negative). I first tried checking Box B -Bond Premium, which you'd think would be the obvious choice, but this didn't affect the tax-exempt interest total. After the workaround Box 10 remains flagged as an error, but I don't think this is a problem. You can remove the error flag by adding a minus sign before the Box 10 entry, but I haven't checked out what effect (if any) this would have on the calculations.
