QSplashScreen appears on a different monitor to CMainWindow

I have a 3 monitor setup (laptop plus 2 HDMI monitors), the laptop screen is set as the primary display on the left-hand side.

When the following is run the splash screen appears centred on the laptop display, however the main window appears centred on the 2nd display - its default position appears to be based on the overall width of the desktop.

I would expect the splash screen and main window to both appear on the same monitor.

int main(int argc, char *argv[])
{{{}}
{{  }}{{QApplication app (argc, argv); }}
{{  }}{{QPixmap pixmap (":/bitmap/SPLASH_SCREEN"); }}

{{  }}{{QSplashScreen splash (pixmap);  }}
{{  }}{{splash.show (); }}
{{  }}{{app.processEvents (); }}
{{  }}{{QTimer::singleShot (1500, &splash, &QWidget::close);   }}
{{  }}{{CMainWindow w; }}
{{  }}{{w.show();  }}
  return (app.exec());
}