PolyHarp got released a while ago, but meanwhile little bugs keep popping up in the MIDI department.
Most of those have to do with the fact that a lot of MIDI synths would like a note off after a while. A note off is really kind of independent of a note on. PolyHarp has a timer that starts with note ons to shut them off after a while . The natural way to turn them off is when they are damped or run out of energy. You can't test the energy of a MIDI note, which is why PolyHarp just scheduled a Note Off.
There was a bug where I was scheduling too many note offs that I fixed a few weeks ago, but there's a more subtle bug:
Play one note and play it again .. the first note's scheduled note off would shut off the new note prematurely. I've now fixed this in PolyHarp 1.0.5