This week, the Philadelphia Orchestra played Vienna’s famed Musikverein, and by coincidence, the ensemble’s old music director, Riccardo Muti, just happened to be staying at a hotel right across the street from the concert hall. Yet strangely, Muti didn’t attend either of the Philadelphians’ concerts, and other than a quick dinner with a violinist and a hastily scheduled meeting with orchestra president Joe Kluger, no one in the orchestra even caught a glimpse of him. In fact, since leaving Philadelphia in 1992, Muti has declined multiple invitations to return to the podium there. Orchestra officials insist that the maestro has a standing invitation.