That issue seems to be corrected with the latest version of TurboTax Desktop. You may want to verify that you are using the most recent version, I think I noticed that it was corrected yesterday or the day before on mine. If you are using the latest version, try deleting out the 1098s and re-entering a fresh one to see if it calculates correctly.
Prior to it being corrected, I had been advising people to enter the mortgage origination date as the original purchase date on homes bought before December 15, 2017 and then answer No to that question to apply the correct mortgage limit. This would only cause an issue if they have points to amortize over the life of a refinanced loan.
In regards to your other question, the only thing reported to the IRS is your deductible home mortgage interest. Whatever you entered as your outstanding mortgage principal or which of the IRS-approved methods you used to determine your balance may be happening in the background on some of the worksheets. The important thing is that you can provide justification for the numbers you report.
@taxissues
