Using QWidget::setMask with complicated QRegion introduces undesired transparent lines when using scaling 125%

Hello!

I encountered following problem when using 125% scaling together with rounded rectangle set as mask with QWidgets::setMask the mask has invisible rows of pixels which should not be there. See attached screens.

My observations:

• Mask scale properly for scaling 100%, 150%, 175%, and 200%. The problem is only in 125%.
• it does not matter whether mask is passed as QRegion or QBitmap

// Add rounded corners using setMask to QDialog    
QDialog* dialog = new QDialog();
dialog->resize(600,400);
QBitmap mask(dialog->size());
mask.clear();
QPainter p(&mask);
p.setRenderHint(QPainter::Antialiasing);
p.setPen(QColor(Qt::black));
p.setBrush(QColor(Qt::black));
p.drawRoundedRect(dialog->rect(), 50, 50);
dialog->setMask(mask);
dialog->exec();