I don't know about others, but for me I think it's just an oddity in the way Schwab does its muni reporting. For a couple of munis Schwab is throwing off offsetting small Box 6 and Box 11 amounts on the OID form, and then puts the bond premium from my acquisition price on 1099-OID instead of on 1099-INT where the interest payment is. I usually have some larger Box 11 from zero coupon munis so I just adjust the 1099-OID and move on, otherwise I'd adjust the 1099-INT. The amounts are small and it all just ends up as one line on state tax as an addition so I don't spend too much time on it.
