attaching a QwtPlotSvgItem to a plot does not work

Code:

QwtPlot myPlot;
    //...
 
    QwtPlotSvgItem bla("test");
    // https://upload.wikimedia.org/wikipedia/commons/0/02/SVG_logo.svg
    if (!bla.loadFile(QRectF(0,0,640,480), "e:/SVG_logo.svg"))
        qDebug("fail to load?");
    else
        qDebug("load OK");
 
    bla.attach(myPlot);

Also a stripped down svg fails:

Code:

<?xml version="1.0" ?>
<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN" "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd">
<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" width="100%" height="100%" viewBox="0 0 100 100">
<rect
        id="background"
        fill="#FF9900"
        width="100"
        height="100"
        rx="4"
        ry="4"/>
          </svg>

Fails means: it is not displayed. It loads fine (true is returned).