Issue is easily seen with the application below and following next steps:
1. launch application
2. click application. That creates new widget with same geometry on top of current.
3. close created widget
4. change resolution (try several) of the screen. Don't move application
5. click application. New widget is created BUT to the wrong position.

#include <QApplication>
#include <QtWidgets>

class MyWidget : public QWidget
{
	void mousePressEvent(QMouseEvent* e)
	{
		QWidget* w = new QWidget();
		w->setGeometry(geometry());
		w->show();
	}
};

int main(int argc, char *argv[])
{
	QApplication a(argc, argv);
	MyWidget w;
	w.show();
	return a.exec();
}