QLabel with word wrap makes unable to decrease parent items size

class TestWidget: public QWidget
{
public:
    QSize sizeHint() const
    {
        return QSize(300, 300);
    }
    QSize minimumSizeHint() const
    {
        return QSize(100, 100);
    }
};

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

    QDialog dialog;
    auto dialogLayout = new QVBoxLayout(&dialog);

    auto mainWidget = new QWidget;
    auto mainLayout = new QVBoxLayout(mainWidget);
    dialogLayout->addWidget(mainWidget);

    auto label = new QLabel("Test");
    label->setWordWrap(true);
    mainLayout->addWidget(label);

    auto widget1 = new TestWidget;
    widget1->setStyleSheet("QWidget {background-color:red;}");
    auto scroll1 = new QScrollArea;
    scroll1->setWidget(widget1);
    scroll1->setWidgetResizable(true);
    mainLayout->addWidget(scroll1);

    auto widget2 = new TestWidget;
    widget2->setStyleSheet("QWidget {background-color:green;}");
    auto scroll2 = new QScrollArea;
    scroll2->setWidget(widget2);
    scroll2->setWidgetResizable(true);
    mainLayout->addWidget(scroll2);

    dialog.show();

    return a.exec();
}