This is not a bug.
IRS requires details to be listed on Form 8949,
or on your own forms (e.g. consolidated 1099-B) which have the same information and in the same manner as Form 8949.
Either way, if you choose to summarize, you have to mail the transaction details to the IRS within three business days of IRS accepting your tax return.
Your return will still have Forms 8949 to e-File but they will have only subtotals instead of each individual transaction.
Form 8453 is just a cover sheet you will include when you have made the mail-in election. It is not to be signed.
