Why has my New Jersey tax amount changed dramatically after filing married jointly?

We did not know that we only had to file one joint return under one account when MFJ, and when we found out, we started working on compiling all the income information to one account to file jointly.

Before we combined the incomes, NJ state tax information showed:

Income
Wages and Salaries: 27284

Personal exemptions: 2000

Taxes
New Jersey Income tax: 1876
nonresident subtraction from income tax: -1282 (we live in NY and I work in NJ, my husband does not)

Credits: none

Payments
New Jersey Tax withholding: 870
Estimated and other payment: 0

However, after we combined all our income information into one, now NJ tax information shows:

Income
Wages and Salaries: 27284

Exemptions: 2000

Taxes
New Jersey Income tax: 10176
Nonresident Subtraction from Income tax: -8962

Credits: none

Payments
New Jersey Tax withholding: 870
Estimated and other payments: 0

How come our New Jersey income tax and Nonresident subraction from income tax has jumped so much after compiling our income data together under one account?

Thanks!