I think I can tell you more precisely here things get astray:
In the "Payment Card and Third Party Network Transactions Worksheet" there is a section "1099-K Reconciliation"
This has 1 - gross amount, 2 - less adjustments 3 - net amount of payment card/third party network transactions
In my example, these would be (1) = $4,400, (2b) (sold at a loss) = $2,300, (3) = (1) - (2a/b) = $2,100
Note that all of my sales show, in detail and correctly, on the "Capital Asset Sales Worksheet".
The total of ALL (with gain plus without gain) proceeds shows correctly in the "Brokerage Statement (Form 1099-B or substitute)" (in my example as $4,400).
I believe that there is an inconsistency here, not with the IRS, just internal with turbotax - the "Form 1099-K worksheet" is not an official schedule, but the check on that field there should either match with the TOTAL of the proceeds from the capital asset sales, or at least it shouldn't be checked against that for multiple mixed gain/loss sales. The IRS will only look at the income or at the data of the cap asset sales' gains.
Since even in that worksheet, I cannot overwrite the number, but I know my data was entered correctly, I will disregard the "smart" check error.
