REG 5.8->5.9: When copy-constructing a pixmap with active painters, the device pixel ratio is dropped

   QApplication a(argc, argv);
    QPixmap pm;
    pm = QPixmap(100, 100);
    pm.fill(Qt::red);
    pm.setDevicePixelRatio(2);
    QPainter p;
    p.begin(&pm);
    QPixmap pm2(pm);
    p.end();
    qDebug() << QT_VERSION_STR << pm << '\n' << pm2;

5.9.0 QPixmap(QSize(100, 100),depth=32,devicePixelRatio=2,cacheKey=0x100000003)
 QPixmap(QSize(100, 100),depth=32,devicePixelRatio=1,cacheKey=0x400000001)

5.8.1 QPixmap(QSize(100, 100),depth=32,devicePixelRatio=2,cacheKey=0x100000003)
 QPixmap(QSize(100, 100),depth=32,devicePixelRatio=2,cacheKey=0x400000001)