Why does my NY state tax increase if I add W2 from a different state?

[ramsgusom]

I moved from NY to PA. W2 from each state. When I enter my PA W2, but tax due for NY state increases. How does this make sense? 

When I looked at the individual page - it subtracts the 8k standard deduction from the federal AGI to calculate the New York taxable income. How does this make sense?

[EdithM]

New York initially computes the tax due based on total, federal income.  Then calculates the percentage of this attributable to New York, income either earned while a resident of New York or sourced to New York while a nonresident.  This may cause the tax to go up even if income belonging to another state is entered, a higher tax bracket may be reached in the initial computation of tax.