According to IRS Publication 521, Moving Expenses, "your employer should not include in your wages reimbursements paid under an accountable plan for moving expenses that you:
1. Could deduct if you had paid or incurred them, and
2. Did not deduct in an earlier year.
These reimbursements are fringe benefits excludable from your income as qualified moving expense reimbursements. Your employer should report these reimbursements on your Form W-2, box 12, with Code P.
So, you are correct that the moving expenses included in box 12 with a P should not be included in your taxable income. I would contact your employer for a corrected W-2.
