Disappearing canvas paths

var window = canvas.Window.new([256, 512], "dialog");
var mcanvas = window.createCanvas();
var root = mcanvas.createGroup();
var grp = root.createChild("group");

mcanvas.setColorBackground(1, 1, 1, 1);
var path = grp.createChild("path")
              .setColor(0, 0, 0)
              .setStrokeLineWidth(3)
              .show();

var grpMove = grp.createChild("group")
                 .setTranslation(128, 384);
var grpPath = grpMove.createChild("path")
                     .setColor(0, 0, 0)
                     .setStrokeLineWidth(3)
                     .moveTo(0, 50)
                     .lineTo(0, -50)
                     .show();

var update = func() {
  var time = getprop("sim/time/mp-clock-sec")*2 or 0;

  path.reset()
      .moveTo(128 + math.sin(time) * 50, 128 + math.cos(time) * 50)
      .lineTo(128 + math.sin(time + 3.1415) * 50, 128 + math.cos(time + 3.1415) * 50);

  grpMove.setRotation(-time);

  settimer(func update(), 0.03);
}

update();