After completion of return, W-2 state should NOT change, if client mailing address changes.  Clients moved out of state; I changed address on return - caused Balance Due to state originally lived/worked in during the taxable year, although the address change is for CURRENT year.  Took me a minute to figure out why suddenly a balance due to state; previously showed refund.  Both times this happened (this year) it was a few weeks (and many tax returns) between completion of return and signatures, due to out-of-state move in Feb/Mar.  Forces one to go through all W-2s to ensure correct state for withholding.  Again.  I believe we are all careful about what state withholding is for when entering W-2 data.