QPainter::drawImage randomly(?) omits some images

[Al_]

Hi

I need to print a series of small images (QR codes); 3 * 9 per page, total ~30 pages. The following code is called repeatedly.

QImage bbcode; 
...
#ifdef QT_DEBUG
      painter.setPen(Qt::darkRed);
      painter.drawRect(textRect[Use4bbImage]);
      bbcode.save(QString(QStringLiteral("%1_%2.jpg")).arg(printQuery.value(0).toInt()).arg(printQuery.value(1).toInt()), 0, 100);
      qDebug() << "draw image" << bbcode << bbcode.rect() << "on" << textRect[Use4bbImage];
#endif
      painter.drawImage(textRect[Use4bbImage], bbcode, bbcode.rect());

QImage bbcode; 
...
#ifdef QT_DEBUG
      painter.setPen(Qt::darkRed);
      painter.drawRect(textRect[Use4bbImage]);
      bbcode.save(QString(QStringLiteral("%1_%2.jpg")).arg(printQuery.value(0).toInt()).arg(printQuery.value(1).toInt()), 0, 100);
      qDebug() << "draw image" << bbcode << bbcode.rect() << "on" << textRect[Use4bbImage];
#endif
      painter.drawImage(textRect[Use4bbImage], bbcode, bbcode.rect());

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The debug output:

draw image QImage(QSize(140, 140) )  QRect(0,0 140x140) on QRect(0,0 2000x2000)

draw image QImage(QSize(140, 140) )  QRect(0,0 140x140) on QRect(0,0 2000x2000)

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Strangely, only appproximately half of the images are printed (on some pages almost all, on others only a few). The code above confirms that all three parameters to painter.drawImage are correct: the textRect[Use4bbImage] is the correct QRect (as the darkRed frame is drawn around the place where the image should be placed), the image bbcode exists (as it is correctly saved to a file), bbcode.rect() is always the same size (as per debug output).

I use Qt 5.3.1 on linux (Ubuntu 12.04 LTS). The issue remains whether I print to pdf or whether I print to a real printer.

Any ideas? How should I proceed to find the bug?

Al_