[Bug?] QGraphicsWidget, transparent background, stylesheet

wolfgang p.

What I want is a half-transparent QGraphicsWidget with rounded borders.
I'm trying to achieve this by setting background-color and border-radius in the widgets stylesheet.

But what happens is that the background is drawn TWICE, once inside the rounded borders and once all over the boundingRect of the corresponding graphics-proxy-item.

Here is a simple example (tested with Qt 4.7.3 on win7-32bit):
@
#include <QtGui/QApplication>
#include <QGraphicsView>
#include <QGraphicsScene>
#include <QPushButton>

int main(int argc, char *argv[])
{
QApplication a(argc, argv);
QGraphicsView view;
QGraphicsScene scene(0, 0, 400, 100);

view.setScene(&scene;);
QPushButton w("just a button");
w.setGeometry(0, 0, 400, 100);
a.setStyleSheet("QPushButton {background-color:rgba(0,0,0,127);border-radius:50px}");
scene.addWidget(&w);

view.show();

return a.exec&#40;&#41;;

}
@

I searched around and tried a lot of things (e.g. manipulating the widgets palette), but nothing worked.
I would really like to know if this is a problem with Qt, or if I'm just doing something wrong...