QDialogButtonBox selects buttons wiithout accept role as default

QDialogButtonBox says in it's documentation:

If you want a specific button to be default you need to call QPushButton::setDefault() on it yourself. However, if there is no default button set and to preserve which button is the default button across platforms when using the QPushButton::autoDefault property, the first push button with the accept role is made the default button when the QDialogButtonBox is shown,

But that's not the case. If you add only a cancel button (which has the reject role), it will be the default button.

I created an example, by using the ConfigDialog example. Therefore I added two lines in line 90 of configdialog.cpp:

QDialogButtonBox *buttons = new QDialogButtonBox(QDialogButtonBox::Cancel, Qt::Horizontal, this);
connect(buttons, &QDialogButtonBox::rejected, this, &QWidget::close);

If you start the example and press enter, the dialog closes because of the cancel button.