Property "forward" of Node is non-NOTIFYable

Properties "forward", "right" and "up" of Node component are non-NOTIFYable and can't be used in QML.

To reproduce:
1) Load Simple skinning example (or any other Quick 3D example).
2) Add this code to PerspectiveCamera:

            property var test: up
            onTestChanged:
            {
                console.log("onTestChanged " + test)
            }
            onForwardChanged:
            {
                console.log("onForwardChanged " + test)
            }

Errors:
QQmlExpression: Expression qrc:/main.qml:77:13 depends on non-NOTIFYable properties:
QQuick3DPerspectiveCamera_QML_1::up
qrc:/main.qml:82:13: Cannot assign to non-existent property "onForwardChanged"