Firefox setValueAtTime bug

JavaScript

var context = new AudioContext(),
    osc = context.createOscillator(),
    gain_node = context.createGain();

osc.connect(gain_node);
osc.start(context.currentTime);
gain_node.connect(context.destination);
gain_node.gain.setValueAtTime(0, context.currentTime + 1);
console.log(gain_node.gain.value);
setTimeout(function () {
    console.log(gain_node.gain.value);
}, 4000);