Is Notice period payout taxable?

While leaving my ex company I paid notice pay period as demand draft. Now my current company is paying me the amount but they will tax it under my "Salary" head. I have submitted a written doent from my previous company that I have paid this amount. Why my current company is considering it as INCOME for me whereas it should be a reimburement since I have paid the amount to my previous company on after getting confirmation from my current employer.