title: Qt nested QGraphicsItem coordinates
body: <p>I would expect, from documentation, that this snippet</p>
  <pre><code>MainWindow::MainWindow(QWidget *parent)
      : QMainWindow(parent)
  {
      QGraphicsView *v = new QGraphicsView(new QGraphicsScene);
      setCentralWidget(v);
  
      QGraphicsRectItem *r1 = v-&gt;scene()-&gt;addRect(QRectF(100,100, 200,200), QPen(), QBrush(Qt::red));
      QGraphicsRectItem *r2 = new QGraphicsRectItem(r1);
      r2-&gt;setRect(QRectF(10,10, 50,50));
      r2-&gt;setBrush(QBrush(Qt::blue));
  }
  </code></pre>
  <p>would draw a blue rect <em>inside</em> the red one, instead here is the result:</p>
  <p><img src="https://i.stack.imgur.com/EllB0.png" alt="enter image description here" /></p>
  <p>Do I miss something ?</p>