Why do you ask?  Did a spouse die, by any chance?  I'm not ready to jump to that conclusion. 

Personal representative may revoke joint return election.

A court-appointed personal representative may revoke an election to file a joint return previously made by the surviving spouse alone. This is done by filing a separate return for the decedent within 1 year from the due date of the return (including any extensions). The joint return filed by the surviving spouse will then be regarded as the separate return of that spouse by excluding the decedent's items and refiguring the tax liability.