I think the Sun is letting the Post take the lead on this to distance themselves from any dirty tricks due to the now settled court case with the governor's office.
Setting aside the Atlantic article it seems the person who could gain the most from the rumors, which are now being discussed by the Sun, is Doug Duncan. He's the likely candidate opposite O'Malley for the democrat primary.
It stands to reason that Duncan, or his people, would approach the Post due to its coverage of Montgomery County as a suburb of DC. He could get more traction from them than he could from the Sun as the Sun is clearly endorsing O'Malley as it did in the last election for mayor.
That is definitely a valid theory.