Windows: Animating window opacity does not work if FramelessWindowHint is set for non-translucent windows.

#include <QApplication>
#include <QPropertyAnimation>
#include <QMainWindow>
#include <QPushButton>
#include <QLabel>
#include <QHBoxLayout>

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
    QWidget *mainWindow = new QWidget(0, Qt::WindowFlags(Qt::FramelessWindowHint));

    QHBoxLayout *l = new QHBoxLayout();
    QPushButton *b = new QPushButton("Quit");
    QObject::connect(b, SIGNAL(clicked()), qApp, SLOT(quit()));
    l->addWidget(b);
    l->addWidget(new QLabel(QT_VERSION_STR));

    mainWindow->setLayout(l);
    mainWindow->resize(QSize(500,500));
    QPropertyAnimation* fadeInAnimation = new QPropertyAnimation(mainWindow, "windowOpacity");
    fadeInAnimation->setDuration(1500);
    fadeInAnimation->setStartValue(0.0);
    fadeInAnimation->setEndValue(1.0);
    fadeInAnimation->start();
    mainWindow->show();
    return app.exec();
}