QPainter problem with real printer on linux

[corossig]

Hello,
I want to print line and text on a real printer but this doesn't work all the time, but on fake printer(screen, PDF and PS) this work.

MainWindow::MainWindow(QWidget *parent)
  : QMainWindow(parent){
  QPushButton *b = new QPushButton("Print", this);
  setCentralWidget(b);
  connect(b, SIGNAL(clicked()), this, SLOT(onPrint()));
}
 
void
MainWindow::onPrint(){
  QPrinter p;
  QPrintDialog dialog(&p, this);
  if(dialog.exec() == QDialog::Accepted){
    QPainter *painter = new QPainter(&p);
    painter->drawLine(0,0,0,100);
    delete painter;
  }
}

MainWindow::MainWindow(QWidget *parent)
  : QMainWindow(parent){
  QPushButton *b = new QPushButton("Print", this);
  setCentralWidget(b);
  connect(b, SIGNAL(clicked()), this, SLOT(onPrint()));
}

void
MainWindow::onPrint(){
  QPrinter p;
  QPrintDialog dialog(&p, this);
  if(dialog.exec() == QDialog::Accepted){
    QPainter *painter = new QPainter(&p);
    painter->drawLine(0,0,0,100);
    delete painter;
  }
}

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This piece of code doesn't work all time, sometimes CUPS tell me that job is cancelled, sometimes a line is draw.
Is that someone already had this problem?

If I put "sleep(1);" before delete painter this piece of code works. Complex printing (SvgRenderer and QTextDocument) works too.

Configuration:
-Archlinux up-date
-Qt 4.8.0
-Cups 1.5.0 usblp