Yes, it's normal. What you're missing is that when you started your tax return TurboTax assumed that you did not receive any advance payments, so it gave you the full $2,000 credit, and calculated your tax on that basis. When you told it that you got $1,800 of the credit in advance, it reduced the credit to $200 instead of $2,000 and recalculated your tax, so your tax went up by $1,800.
The little box that shows your refund or tax due while you are working on your tax return is really not meaningful until you have entered everything.
