A DESCRIPTION OF THE PROBLEM :
If MidiDevice.getMaxReceivers()==-1 makes any sense, the receivers should act independently, as if two devices were present.


STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Apply getReceiver() twice on a Gervill soft synthesizer object. Two distinct Receiver objects will be obtained.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
When one receiver changes, say, the sound of MIDI channel 1 to piano, and another receiver changes its MIDI channel 1 to violin, and to each receiver a note is sent, two different sound timbres should be produced.
ACTUAL -
Both notes sound the same.

---------- BEGIN SOURCE ----------
public boolean GetTwoIndependentReceivers (Receiver [] inhereplease)
{
    for (MidiDevice.Info info : MidiSystem.getMidiDeviceInfo ()) try
    {
        MidiDevice device = MidiSystem.getMidiDevice (info);
        if (   device instanceof Synthesizer
            && (   device.getMaxReceivers () < 0
                || device.getMaxReceivers () >= 2)) try
        {
            device.open ();
            inhereplease [0] = device.getReceiver ();
            inhereplease [1] = device.getReceiver ();
            // will be distinct as objects, but with Gervill not independent
            return true;
        } catch (Exception ex) {}
    } catch (Exception ex) {}
    return false;
}
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
I have tried to create two Gervill SoftSynthesizers objects on the same audio line, and one receiver for each. No exception is being thrown, but the resulting audio is a total mess – perhaps yet another bug?