getExistingDirectory doesn not expand directory tree

[franco.amato]

Good evening,
I'm writing a code where I call the getExistingDirectory and the directory tree doesn't expand.
This is the code:

void MainWindow::on_sourceDirBrowseButton_clicked()
{
     QString path = QFileDialog::getExistingDirectory(this, tr("Open Directory"),
                                                     m_application->userDataDir().path()); // This doesn't expand
    if (!path.isEmpty())
    {
        m_application->setSourceDirPaths(QStringList(path));
    }
}

void MainWindow::on_sourceDirBrowseButton_clicked()
{
     QString path = QFileDialog::getExistingDirectory(this, tr("Open Directory"),
                                                     m_application->userDataDir().path()); // This doesn't expand
    if (!path.isEmpty())
    {
        m_application->setSourceDirPaths(QStringList(path));
    }
}

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I'm working under Windows XP.

Any help is appreciated.

Regards,
Franco