Qt ignore click when dismissing popup on Windows - c++

Question

I have an issue with Qt where the behavior on Windows is different than Mac or Linux. I discovered the issue on PySide2 but was able to reproduce it in a minimal C++ application as well (see below).
When I dismiss a Popup widget by clicking outside the click is ignored by the rest of the application. This is the desired behavior and is the way it works on Linux and Mac. However in Windows this click is registered by the widget that was clicked which in my application leads to unwanted user input on the underlying widgets.
Is there a way to will prevent the dismissal click from being passed on in Windows? I am fine with having platform dependent code for this issue.
The behavior can be reproduced with this example. When the popup is open and testButton is clicked the onTestButton method will be executed.
#include "mainwindow.h"
#include <QPushButton>
#include <QHBoxLayout>
#include <QDebug>
MainWindow::MainWindow(QWidget *parent)
: QMainWindow(parent)
{
this->setFixedHeight(600);
this->setFixedWidth(800);
QWidget* w = new QWidget();
QDialog* popUp = new QDialog();
popUp->setFixedHeight(200);
popUp->setFixedWidth(200);
popUp->setWindowFlag(Qt::Popup | Qt::FramelessWindowHint);
popUp->setModal(true);
popUp->setVisible(false);
QHBoxLayout *layout = new QHBoxLayout(this);
w->setLayout(layout);
QPushButton* openButton = new QPushButton("open popup");
// same behavior whether using QDialog::show or QDialog::exec
connect(openButton, &QPushButton::clicked, popUp, &QDialog::show);
QPushButton* testButton = new QPushButton("catch mouse");
connect(testButton, &QPushButton::clicked, this, &MainWindow::onTestButton);
layout->addWidget(openButton);
layout->addWidget(testButton);
this->layout()->addWidget(w);
}
void MainWindow::onTestButton()
{
qDebug() << "caught mouse";
}

Answer 1

QWidget is just a widget, if you want it to "hold" focus, then use QDialog instead.
Also it changes the "logic" if u use it as QDialog.show or QDialog.exec.
Can you try with QDialog?

Answer 2

QDialog::setModal(bool) should set the dialog to modal, thus prohibiting clicking into the mainwindow.
Your windowflag Qt::Popup blocked modality. If you want to use that approach and create Qwidget as a modal dialog (Qt::Dialog), it should be launched from another window, or have a parent and used with the QWidget::windowModality property.
Tested:
auto w = new QWidget;
QDialog* popUp = new QDialog;
popUp->setFixedHeight(200);
popUp->setFixedWidth(200);
popUp->setWindowFlags( Qt::FramelessWindowHint);
popUp->setModal(true);
QHBoxLayout *layout = new QHBoxLayout(this);
w->setLayout(layout);