QFileDialog does not work when run inside an QEventLoop with ExcludeUserInput set

I have a program which disables user inputs at some point to be able to queue them for later. This works fine till I try to show a file dialog (see the attached sample), which (simplified) boils down to:

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    connect(ui->pushButton, &QPushButton::clicked, []() {
        QEventLoop* loop = new QEventLoop;
        QTimer::singleShot(1000, [loop]() {
            QFileDialog::getOpenFileName(qApp->activeWindow(), "test", "/tmp");
            loop->quit();
            loop->deleteLater();
        });
        loop->exec(QEventLoop::ExcludeUserInputEvents);
    });
}

This seems to work on windows but fails horribly on Linux with Glib (window does not paint properly nor reacts to user input). Since QFileDialog internally uses a new eventloop which does not exclude user inputs, I do not understand why this happens. Is this a bug in Qt, are nested event loops like that just not supported, or…? I do realize that my usage here is kinda odd, but I do not see why it could not work.