QFileSystemWatcher::removePaths() Does not removes drive

#include <QtCore/QCoreApplication>
#include <QFileSystemWatcher>
#include <QDebug>
#include <QStringList>

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);
    QFileSystemWatcher* w = new QFileSystemWatcher;
    w->addPath("D:\\");
    auto r = w->removePaths(w->directories());
    qDebug()<<r;// This still prints D:\

    //w->addPath("D:\\tmp");
    // auto r = w->removePaths(w->directories());// This works
    //qDebug()<<r; // prints nothing
    return a.exec();
}