[Linux] Wrong paintings of QPainterPath with CompositionMode_Clear

In the code below, if one changes composition mode or makes rect non-transparent, everything works fine.

Code to reproduce:
//------------------------------------------
#include <QtGui>
#include <math.h>

class Test : public QWidget
{
public:
Test() : QWidget() {}
~Test() {}

protected:
virtual void paintEvent( QPaintEvent * )

{ QPainter pnt( this ); // fill the background of window pnt.fillRect( 0, 0, width(), height(), QBrush( Qt::white ) ); int twidth = 10; int ax = 2*twidth, ay = 2*twidth; QPainterPath tpath; double width = 400+2*twidth; // build the rounded rect with the width '2*twidth' tpath.addRoundedRect( ax-twidth, ay-twidth, width, 2*twidth, twidth, twidth ); // rotate it on PI/4 around on of the ends tpath = QTransform().translate( ax, ay ).rotateRadians( M_PI / 4 ) .translate( -ax, -ay ).map( tpath ); // draw pnt.setBrush( QBrush( Qt::transparent ) ); pnt.setCompositionMode( QPainter::CompositionMode_Clear ); pnt.drawPath( tpath ); }

};

int main( int argc, char * argv[] )
{
QApplication app( argc, argv );
Test t;
t.show();
return app.exec();
}
//------------------------------------------