macOS: Wrong cursor shown when the mouse is moved slowly into window

When moving the mouse slowly into the window across the border, the cursor becomes an arrow cursor instead of the set cursor.
If it is moved into the window through the title bar or really fast across the window border, the set cursor is correctly shown.

In the example below showing this behaviour, the cursor is set on a widget in a QMainWindow.
If the cursor is set directly on the QMainWindow and not the central widget, it seems to work as expected.
 

#include <QApplication>
#include <QMainWindow>
#include <QWidget>

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

    QWidget *widget = new QWidget;
    widget->setCursor(QCursor(Qt::CrossCursor));

    QMainWindow mainWindow;
    mainWindow.setCentralWidget(widget);
    mainWindow.resize(500, 500);

    mainWindow.show();
    return app.exec();
}