QComboBox - minimumSizeHint issue

// Qt 5.15, QComboBox implementation
...
/*! \reimp */
void QComboBox::changeEvent(QEvent *e)
{
    Q_D(QComboBox);
    switch (e->type()) {
    case QEvent::StyleChange:
        d->updateDelegate();
#ifdef Q_OS_MAC
    case QEvent::MacSizeChange:
#endif
        d->sizeHint = QSize(); // invalidate size hint
        d->minimumSizeHint = QSize();
        ...
        break;
    case QEvent::FontChange: {
        d->sizeHint = QSize(); // invalidate size hint
        /* d->minimumSizeHint = QSize(); it is necessary too !!! */
        d->viewContainer()->setFont(font());
        d->viewContainer()->itemView()->doItemsLayout();
        if (d->lineEdit)
            d->updateLineEditGeometry();
        break;
    }
    default:
        break;
    }
    QWidget::changeEvent(e);
}
...

// Qt 5.15, QAbstractSpinBox implementation
...
bool QAbstractSpinBox::event(QEvent *event)
{
    Q_D(QAbstractSpinBox);
    switch (event->type()) {
    case QEvent::FontChange:
    case QEvent::StyleChange:
        d->cachedSizeHint = d->cachedMinimumSizeHint = QSize();
        break;

    ...
    }
    return QWidget::event(event);
}