Binding evaluates value even !when

import QtQuick 2.0

Rectangle {
    id: root
    width: 300
    height: 400

    Binding {
        target: root
        property: "color"
        value: loader.item.color
//        value: loader.item ? loader.item.color : "white"
        when: Qt.isQtObject(loader.item)
    }

    Loader {
        id: loader
        anchors.centerIn: parent
    }

    MouseArea {
        anchors.fill: parent
        onClicked: loader.sourceComponent = rect
    }

    Component {
        id: rect
        Rectangle {
            width: 100
            height: 100
            color: "blue"
            border.color: "yellow"
            border.width: 5
        }
    }
}