Here is the official way it should be done:
You file a PA non-resident return declaring the income earned while working in PA. Since there was no withholding, you will owe quite a bit. If you had 401k deductions, use the Medicare wages as your PA income.
Then you prepare a DE resident return declaring all your income, including that earned in PA. You also request a credit for taxes paid to another state (from your PA return). Since he withheld for only DE, you should receive a significant refund.
