Transparent QQuickView doesn't clear graphics buffer when moved

// main.cpp
#include <QGuiApplication>
#include <QQuickView>

int main(int argc, char *argv[])
{
    QGuiApplication app(argc, argv);
    QQuickWindow::setDefaultAlphaBuffer(true);

    QQuickView view;
    view.setSource(QUrl("main.qml"));
    view.setColor(QColor(0, 0, 0, 0)); // For transparency
    view.show();

    return app.exec();
}

// main.qml
import QtQuick 2.0

Rectangle {
    width: 600
    height: 480
    color: "transparent"
    
    Rectangle {
        width: 300
        height: 240
        anchors.centerIn: parent
        color: "red"
        opacity: 0.5
    }
}