QComboBox up and down arrow scroll controls does not disappear once they are shown for the first time

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
}

MainWindow::~MainWindow()
{
    delete ui;
}

void MainWindow::on_pushButtonLongList_clicked()
{
    int count = 100;

    ui->comboBox->clear();
    for (int i = 1; i < count; ++i) {
        ui->comboBox->insertItem(ui->comboBox->count(),"Value"+QString::number(i));
    }
}

void MainWindow::on_pushButtonShortList_clicked()
{
    int count = 4;
    ui->comboBox->clear();

    for (int i = 1; i < count; ++i) {
        ui->comboBox->insertItem(ui->comboBox->count(),"Value"+QString::number(i));
    }
}

ui->comboBox->view()->setVerticalScrollBarPolicy(Qt::ScrollBarAsNeeded);