Hardware MIDI Polyphony requires twice as many voices as necessary

[DBraun]

I'm using a MIDI controller. If I use faust code for 6 voices and select 6 voices for the Nvoices custom parameter, it only yields 3 effective voices.

declare options "[midi:on]";
declare options "[nvoices:6]";
import("stdfaust.lib");

freq = hslider("freq",60,36,96,1) +24 : ba.midikey2hz;
gain = hslider("gain",1,0,1,0.01);
gate = button("gate");
envelope = en.adsr(0.1,0.2,0.9,0.3,gate)*gain;

panVal = hslider("pan[midi:ctrl 41]", 0,0,1,.01) : si.smoo;

process = os.osc(freq)*envelope : sp.panner(panVal) <: _,_;

effect = dm.zita_light ;

If I set the parameters and code to 8 voices, I get just 4.