QMenu pops up on wrong screen

 #include <QApplication>
 #include <QPushButton>
 #include <QMenu>
 #include <QAction>

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

auto b = new QPushButton(&w);
 QObject::connect(b, &QPushButton::clicked, &w, [b](bool)

{ auto m = new QMenu(b); m->addAction("action 1"); m->popup(b->mapToGlobal(QPoint(0, b->height()))); }

);

w.show();
 return a.exec();
 }