Bug? AndroidGlue can't playback two channel together

[KyoSherlock]

I want to develop a real time MIDI.
midi.onProgramChange(0, 1); // e.g. piano
midi.onNoteOn(0, 60, 80);
midi.onProgramChange(1, 1); // e.g. woodblock
midi.onNoteOn(1, 60, 80);
If they playback a same key(e.g. 60) at the same time. the sound is cut off.