Numeric keypad entry does not respect Num Lock state

After upgrading my application from the 5.9.x release series to 5.12.4, I found that keyboard input using the numeric keypad does not respect the Num Lock state. Specifically, the QKeyEvents that are passed to QWidget::keyPressEvent() always contain a key() value that represents the key's meaning when Num Lock is off (for instance, pressing the 9 key always sends a Key_PageUp event, regardless of the state of Num Lock).

This is a little similar to a previous bug in 5.1.0: https://bugreports.qt.io/browse/QTBUG-32687. The same test program provided there suffices to duplicate the issue:

Built with: g++ -o test test.cpp $(pkg-config --cflags --libs Qt5Core Qt5Gui Qt5Widgets) -fPIC

#include <QApplication>
#include <QDoubleSpinBox>
#include <QMainWindow>

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

    QApplication a(argc, argv);

    QMainWindow w;

    w.setCentralWidget(new QDoubleSpinBox(&w));

    w.show();

    return a.exec();
}

This will open a window with a QDoubleSpinBox in it. Try using the numeric keypad to enter a value into it and you'll find that the keys all act as arrow/navigation keys, no matter whether Num Lock is on or off.

There was a similar report with Qt 5.12 here: https://forum.freecadweb.org/viewtopic.php?style=3&f=4&t=35102