PRECONDITION

1. A MidiDevice providing the default Receiver (or Transmitter) is supplied via the service provider interface (using javax.sound.midi.spi.MidiDeviceProvider).
2. The Receiver (or Transmitter) does not implement MidiDeviceReceiver (or MidiDeviceTransmitter).
3. The Receiver (or Transmitter) implementation overrides methods from java.lang.Object.

PROBLEM

  System.setProperty("javax.sound.midi.Receiver", /* Our receiver */);
  Receiver receiver = MidiSystem.getReceiver();

  // THESE METHODS ARE NOT INVOKED FROM THE RECEIVER IMPLEMENTATION!
  receiver.toString();
  receiver.equals();
  receiver./* Any other method from java.lang.Object */


INITIAL ANALYSIS

From the RI code:
    public static Receiver getReceiver() throws MidiUnavailableException {
        // . . .
        if (!(receiver instanceof MidiDeviceReceiver)) {
            receiver = new MidiDeviceReceiverEnvelope(device, receiver);
        }
        return receiver;
    }
It looks like MidiDeviceReceiverEnvelope does not forward java.lang.Object methods to veritable receiver.