Working on 2021 tax and have this same problem.
I think TT does not handle this situation properly at all.
Best I can tell - this situation arises when you purchase a muni bond on secondary market at a premium (price above 100%), when the bond was originally issued at a price below par (less than 100%).
I am not a tax expert, and this is pretty confusing - but, I think what is happening is that the 1099OID is reporting in box 11 the amount you should increase your taxexempt income by IF you purchased the bond at issue/at a discount to par. Which is not the case. So, box 6, acquisition premium matches box 11 and offsets.
Box 10 - bond premium is the amount of tax exempt income Schwab reported for this issue that's included in 1099INT Box 8. BUT Schwab has NOT reported the bond premium associated with this issue in 1099INT box 13 (bond premium on tax-exempt bond), and the amount reported on 1099OID box 10 SHOULD reduce the amount of your tax-exempt interest.
This can be important both for State Tax calculations and other issues like tax on social security and your medicare part B premium adjustment because tax-exempt income IS included in adjusted income used for these (and other) things.
So, TurboTax fails to deal with this, and I'm still trying to figure out how to adjust things so it's treated properly.
