And the answer is, NO, the error has not been corrected.
The Federal mortgage interest worksheet now computes the Federal mortgage deduction limit correctly.
The corresponding California step-b-step is now asking for the ending balances on original and refi loans, which is a step (so to speak) forward, but it's still not calculating the two average balances correctly. The mortgage Ded Home Mort worksheet is still not pro-rating the original and refinanced mortgages correctly; rather, it's doing (begin-end)/2 calculation for the original loan (which means it's in effect assuming a June 30 refi), but it's doing an (orig-end)/2 calculation for the refi, which would only be correct if the refi were on Jan 1. So it's still overestimating the average balance of all home acquisition debt.
The error can be corrected manually by overriding the "average balance" entries in the "Above debt categorized..." section, substituting the correctly prorated average balances calculated by the Federal form.
In my case (mortgage originally taken out before Dec 2017, and then refinanced in 2019, both loans >$1m), the calculations should be almost identical for Federal and California returns. The only difference is that the Feds allow me to deduct interest on no more that $1m of average mortgage balance, whereas California allows an additional $100k for a $1.1m cap. Only the limits, and not the balance calculations, are different for someone whose original loan came before Dec 2017.
But in either case the calculations for average balances should be identical between Fed and CA, and I really wish TurboTax would get on the ball and fix this so we don't have to override to get correct tax calculations.
