I used TurboTax desktop software and submitted tax file to IRS electronically. For my tax return, I imported all trading information (include stocks and market discounted US government bond) from my brokerage account into TurboTax software, I did not use summary methods, so all the trading information were directly imported to form 8949 in TurboTax which were then attached to form 1040 and was filed to IRS electronically. However, after electronic filing, the TurboTax told me that I need to fill out form 8453, and mail the form 8453 and form 8949 together to IRS. This issue never happened in previous years, why it happens this year?
