Layout - dirty label

I'm studying the tutorials and I have run into something unexpected.

This is the code taken from Layout tutorial. I only changed the setLabel text (One → One11111, Two → Two22222:

var Layout = require("Layout");
var layout = new Layout({
  type: "v",
  c: [{
      type: "txt",
      font: "6x8:2",
      label: "A Test",
      id: "label"
    },
    {
      type: "btn",
      font: "6x8:2",
      label: "One",
      cb: l => setLabel("One11111")
    },
    {
      type: "btn",
      font: "6x8:2",
      label: "Two",
      cb: l => setLabel("Two22222")
    }
  ]
}, {
  btns: [{
    label: "Three",
    cb: l => setLabel("Three")
  }],
  lazy: true
});

function setLabel(x) {
  layout.label.label = x;
  layout.render();
}
g.clear();
layout.render();

After the second click the label gets dirty (both on emulator and physical device). What's wrong?

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