Qt3D Warning: Created graphical object was not placed in the graphics scene

import QtQuick

// as soon as this import is added, warnings appear
import Qt3D.Core as Unused

Window {
    width: 640
    height: 480
    visible: true

    // if 'target' and 'child' are Items no warning appears
    // if at least one is a QtObject a warning does appear
    Item {
        id: target
    }

    Component {
        id: child

        QtObject {}
    }

    Component.onCompleted: {
        child.createObject(target);
    }
} 

QQmlPrivate::RegisterAutoParent autoparent = { 0, &qquick3ditem_autoParent };
QQmlPrivate::qmlregister(QQmlPrivate::AutoParentRegistration, &autoparent); 

static QQmlPrivate::AutoParentResult qquick3ditem_autoParent(QObject *obj, QObject *parent)
{
    auto parentNode = qmlobject_cast<Qt3DCore::QNode *>(parent);
    if (parentNode) {
        auto node = qmlobject_cast<Qt3DCore::QNode *>(obj);
        if (node) {
            // A QNode has another QNode child
            node->setParent(parentNode);
            return QQmlPrivate::Parented;
        }
    // FIX: the following line should be
    // } else if (qmlobject_cast<Qt3DCore::QNode *>(obj)) {
    } else {
        return QQmlPrivate::IncompatibleParent;
    }
    return QQmlPrivate::IncompatibleObject;
}