QFontMetrics reports wrong size for substitution (box) character

In the example below, the box-character that substitutes glyphs that are not part of the installed fonts

#include <QtGui>

class Widget : public QWidget
{
public:
Widget()
{
}

void setString(const QString &str)

{ string = str; update(); }

protected:
void paintEvent(QPaintEvent *event)
{
QPainter painter(this);
int x = 0;
int y = painter.fontMetrics().height();
for (int c = 0; c < string.length(); ++c)

{ QChar ch = string.at(c); qDebug() << ch.unicode() << painter.fontMetrics().width(); painter.drawText(x, y, ch); x += painter.fontMetrics().width(); }

}

private:
QString string;
};

int main(int argc, char *argv[])
{
QApplication a(argc, argv);
QFont font("Tahoma", 36);
a.setFont(font);

QString unicode;
unicode += QChar(0x0061);
unicode += QChar(0x028c);
unicode += QChar(0x0303);
unicode += QChar(0x0020);
unicode += QChar(0x0303);
unicode += QChar(0x4100);
unicode += QChar(0x901F);
unicode += QChar(0x3100);
unicode += QChar(0x0010);
unicode += QChar(0x00CA);
unicode += QChar(0xF053);
unicode += QChar(0x2112);
unicode += QChar(0x0062);

QLineEdit le;
le.setText(unicode);

QLabel label;
label.setText(unicode);

Widget w;
w.setString(unicode);

w.show();
label.show();
le.show();

return a.exec();
}

When turning font subtitution off, then QLineEdit and QLabel render the text with proper spacing, but QFontMetrics still returns a value that is too small.