[MacOSX] QIcon doesn't display properly on HighDPI screen when one screen is HighDPI and one is not

I have two 24" monitors whose native resolution is 1900x1080.

If I run the attached test application, the two icons displayed in the dialog the application creates look correct (test_nohighres_monitor.png).

If I then change my left monitor's resolution to simulate a retina display (960x540 HiDPI) and restart the application, the icons look correct when the application is on the left (simulated HiDPI) monitor (test_highres_monitor.png) but if I move the application to the right, native resolution monitor, some icons look very bad (test_lowres_monitor.png, focus on the icon on right).

As you can see in the test application, for each image I have a regular version and a @2x version.

I would expect that when I move the application from the HiDPI monitor to the regular DPI monitor, the icon file being displayed would go from the @2x version to the regular version.

I'm not sure what is actually happening, however. It sort of looks like the 32x32 pixel @2x icon is being used but scaled down to 16x16 pixels, but not quite.

The code in the test application is:

int main(int argc, char *argv[])
{
	QApplication a(argc, argv);

#if QT_VERSION >= 0x050100
	a.setAttribute(Qt::AA_UseHighDpiPixmaps, true);
#endif

	QDialog modalD;
	modalD.setModal(true);

	// Create buttons.
	QPushButton* pb1 = new QPushButton(&modalD);
	pb1->setIcon(QIcon(":/Icons/go-home.png"));

	QPushButton* pb2 = new QPushButton(&modalD);
	pb2->setIcon(QIcon(":/Icons/x-office-document.png"));

	// Use a layout.
	QHBoxLayout* hLayout = new QHBoxLayout();
	hLayout->addWidget(pb1);
	hLayout->addWidget(pb2);
	modalD.setLayout(hLayout);

	modalD.setWindowTitle("Modal dialog");
	modalD.exec();

	return a.exec();
}