Wrong z-order in scene rendererd by QQuickRenderControl

#include <QtGUi/6.6.1/QtGui/rhi/qrhi_platform.h>
#include <QtGui/6.6.1/QtGui/rhi/qrhi.h>
#include <QtQuickWidgets>

class OffscreenRenderer : public QLabel {

public:
    OffscreenRenderer()
    {
        setMinimumSize(10, 10);
        setScaledContents(true);

        window.setColor(Qt::transparent);

        QQmlComponent component{&engine, QUrl{"qrc:/App/Main.qml"}};
        item.reset(static_cast<QQuickItem *>(component.beginCreate(engine.rootContext())));
        item->setParentItem(window.contentItem());

        component.completeCreate();
        control.initialize();
    }
private:
    auto resetTexture() noexcept -> void
    {
        auto rhi = control.rhi();
        const auto size = window.size();
        texture.reset(rhi->newTexture(QRhiTexture::RGBA8, size, 1, QRhiTexture::RenderTarget | QRhiTexture::UsedAsTransferSource));
        qDebug() << texture.get();
        if (!texture->create())
            qFatal() << "failed to create texture";
        depthStencil.reset(rhi->newRenderBuffer(QRhiRenderBuffer::DepthStencil, size, 1));
        if (!depthStencil)
            qFatal() << "failed to create depth-stencil buffer";
        QRhiTextureRenderTargetDescription desc{QRhiColorAttachment{texture.get()}, depthStencil.get()};
        rtt.reset(rhi->newTextureRenderTarget(desc));
        pass.reset(rtt->newCompatibleRenderPassDescriptor());
        rtt->setRenderPassDescriptor(pass.get());
        if (!rtt->create())
            qFatal() << "failed to create render target";
        window.setRenderTarget(QQuickRenderTarget::fromRhiRenderTarget(rtt.get()));
    }
    auto resizeEvent(QResizeEvent *event) -> void final
    {
        window.resize(size());
        item->setSize(size());
        resetTexture();
        render();
        QLabel::resizeEvent(event);
    }
    auto render() noexcept -> void
    {
        if (!rtt)
            return;
        control.polishItems();
        control.beginFrame();
        control.sync();
        control.render();

        auto rhi = control.rhi();
        QRhiReadbackResult readResult;
        QRhiResourceUpdateBatch *readbackBatch = rhi->nextResourceUpdateBatch();
        readbackBatch->readBackTexture(texture.get(), &readResult);
        control.commandBuffer()->resourceUpdate(readbackBatch);

        control.endFrame();

        QImage image(reinterpret_cast<const uchar *>(readResult.data.constData()),
                     readResult.pixelSize.width(),
                     readResult.pixelSize.height(),
                     QImage::Format_RGBA8888_Premultiplied);
        setPixmap(QPixmap::fromImage(image.copy())); // detach
    }
    QQmlEngine engine;
    QQuickRenderControl control;
    QQuickWindow window{&control};
    std::unique_ptr<QQuickItem> item;
    std::unique_ptr<QRhiTexture> texture;
    std::unique_ptr<QRhiRenderBuffer> depthStencil;
    std::unique_ptr<QRhiTextureRenderTarget> rtt;
    std::unique_ptr<QRhiRenderPassDescriptor> pass;
    QTimer timer;
};

int main(int argc, char **argv) {
    QApplication app{argc, argv};

    QWidget w;
    auto hbox = new QHBoxLayout;
    w.setLayout(hbox);

    auto renderer = new OffscreenRenderer;
    hbox->addWidget(renderer);

    auto qw = new QQuickWidget{&w};
    qw->setSource(QUrl{"qrc:/App/Main.qml"});
    qw->setResizeMode(QQuickWidget::SizeRootObjectToView);
    hbox->addWidget(qw);

    w.resize(800, 400);
    w.show();

    return app.exec();
}

import QtQuick

Item {
    id: root

    Rectangle {
        id: red
        anchors.fill: parent
        color: Qt.rgba(1, 0, 0, 0.3)
    }

    Rectangle {
        id: white
        color: 'white'
        width: parent.width * 0.2
        height: width
    }
}