I have the same concern so I have to really look for what it means. This is what I found:
Is there a limit to the amount I can deduct?
Yes, your deduction is generally limited if all mortgages used to buy, construct, or improve your first home (and second home if applicable) total more than $1 million ($500,000 if you use married filing separately status) for tax years prior to 2018. Beginning in 2018, this limit is lowered to $750,000. Mortgages that existed as of December 14, 2017 will continue to receive the same tax treatment as under the old rules.
So, it means there's a limit 750,000. Any number here lower than it should be able to deductible. I believe most people's mortage is so, thus, copy line 1 to line 2 is ok. But why is it a problem at the first place? Apparently, the system has bug on refinance. It acts like we didn't refinance, instead we have another mortage. If you had 2 houses, each has a 500,000 mortgage and deduct full amount of the first one, then the second one can only deduct 750,000-500,000=250,000.
Anyway, I won't become a hater of turbox tax for just one bug. Please fix it, Turbo!
