QPushButton::released event is not handled

// window.h
#ifndef WINDOW_H
#define WINDOW_H
#include <QWidget>
QT_BEGIN_NAMESPACE
class QLabel;
class QLineEdit;
class QProgressBar;
class QPushButton;
class QFrame;
class QCheckBox;
QT_END_NAMESPACE
class Window : public QWidget
{
    Q_OBJECT
    
public:
    Window(QWidget *parent = nullptr);
    
public slots:
    void editingFinished();
    void buttonPressed();
    void buttonReleased();
    
private:
    void updateImage();
    
    bool abortFlag_{ false };
    bool isRunning_{ false };
    QLabel *btnStateLbl_{ nullptr };
    QLineEdit *le1_{ nullptr };
    QProgressBar *progress_{ nullptr };
    QFrame * mainFrame_{ nullptr };
};
#endif

// window.cpp
#include "window.h"
#include <QApplication>
#include <QBrush>
#include <QCheckBox>
#include <QElapsedTimer>
#include <QLabel>
#include <QLineEdit>
#include <QPainter>
#include <QPixmap>
#include <QProgressBar>
#include <QPushButton>
#include <QRect>
#include <QVBoxLayout>
#include <QValidator>

Window::Window(QWidget *parent)
    : QWidget(parent)
{
    setWindowTitle(tr("Sample"));
    QVBoxLayout *vbox = new QVBoxLayout;
    le1_ = new QLineEdit;
    vbox->addWidget(le1_);
    QPushButton *btn1 = new QPushButton("Dummy (Does nothing)");
    vbox->addWidget(btn1);
    btnStateLbl_ = new QLabel("Button State:");
    vbox->addWidget(btnStateLbl_);
    mainFrame_ = new QFrame;
    mainFrame_->setLayout(vbox);
    vbox = new QVBoxLayout;
    vbox->addWidget(mainFrame_);
 
    progress_ = new QProgressBar();
    vbox->addWidget(progress_);
    connect(le1_, &QLineEdit::editingFinished,
            this, &Window::editingFinished);
    connect(btn1, &QPushButton::pressed,
            this, &Window::buttonPressed);
    connect(btn1, &QPushButton::released,
            this, &Window::buttonReleased);

    setLayout(vbox);
}

void
Window::editingFinished()
{
    updateImage();
}
void
Window::buttonPressed()
{
    btnStateLbl_->setText("Button State: Pressed");
}
void
Window::buttonReleased()
{
    btnStateLbl_->setText("Button State: Released");
}

void
Window::updateImage()
{
    if (isRunning_) {
        return;
    }
    isRunning_ = true;
    // We assume for the purposes of this example that updating the image takes
    // a long time.
    QElapsedTimer timer;
    timer.start();
    static constexpr int totalMsec{ 2000 };
    progress_->setRange(0, totalMsec);
    while (totalMsec >= timer.elapsed()) {
        progress_->setValue(timer.elapsed());
        qApp->processEvents();
    }
    progress_->reset();
    isRunning_ = false;
}