We'll have to look into it once we get more information. I don't believe that play/stop messages are being normally generated by the PF. The fact that they are very similar to MIDIclock messages may be relevant – if MIDIclock is getting corrupted by either the sender or the receiver it might explain things.
Can you try just connecting your PF to MIDI-OX ? I tried this and cannot duplicate your problem. It may be associated with your other equipment and thus be hard for us to see.
