Ann: Ceasing to be a substantial holder from MS, page-42

I'm not so sure about the reasons MM hasn't converted yet.

Trading your company stock in a takeover period is not really the look most CEOs want to present to their shareholders. Whatever his views as to another bidder emerging (for which I imagine his public view would be neutral/negative), I reckon he feels it is only proper to sit on his hands until the proposed transaction is complete, and convert at that time per the prescribed process. He's a dead straight shooter.