This seems like the same problem I'm having with one state return. Extension payment for 2017 $ 4000 paid in 2018, refund $ 6842, Turbo tax says $ 5322 taxable, but I thought it should be $ 2842. We itemized on 2017 return and didn't on 2018. TT questions just ask how much was paid with extension but NOT when it was paid.
