Using an example:
You moved to FL May 1 and continued to work for the same employer all year. The employer withheld for PA thru June 1. You will file a part year resident PA return and report all your income for Jan 1 to May 1. Because the amount your report as PA income, on your tax return, will be less than the amount shown in box 16 of your W-2, there's a chance you will get a dunning letter from the PA Dept of Revenue. Then you'll have to convince them of the error.
The above assumes you work at your employer's facility in FL. If your are a telecommuter, the rules are different. PA is one of the hand full of states that tax telecommuters working for PA companies. If you work outside the state as a job requirement, you are only subject to PA State income tax on the days you work in PA. But if you work outside PA for your own convenience, you are subject to PA State income tax on all your income. New York, Nebraska, Delaware and New Jersey have the same rule. For guidance see: http://www.journalofaccountancy.com/issues/2009/jun/20091371.html
