In MK 5.3.1, the Conductor now runs on a Separate
Thread, however, it can no longer communicate with the
application thread to perform screen updates (such as
highighting a measure of score during playback).
Currently an error message is displayed indicating
that MusicKit "Should be sending message back to
application thread, unimplemented"
If the conductor does not run on a separate thread,
application updates occur, but timing problems result.