C++/Qt5 Show underscore on button caption - Windows 10

[jimbo]

Hello,

Windows 10
Qt Creator 3.6.1
Based on Qt 5.6.0

void MainWindow:: on_button_clicked()
{
    ...
    QPushButton *pb = new QPushButton("&Close", choice);
    pb->setGeometry(22, g1->x() + g1->height() + 5, 70, 25);
    QObject::connect(pb, SIGNAL(clicked()), this, SLOT(pb_clicked()));
    ...
}

void MainWindow:: on_button_clicked()
{
    ...
    QPushButton *pb = new QPushButton("&Close", choice);
    pb->setGeometry(22, g1->x() + g1->height() + 5, 70, 25);
    QObject::connect(pb, SIGNAL(clicked()), this, SLOT(pb_clicked()));
    ...
}

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Alt + C works.
The underline doesn't show on the 'C' in the button caption.
Is this a problem with the fonts in Windows 10?
Is there a way round it?

Regards

Edited - Changed Ctrl for Alt.