The size of an array declared as a QML object property can't be altered directly

import Qt 4.6

Rectangle {
    width: 640
    height: 480
    id: rect
    property var array: new Array

    Rectangle {
        height: 50
        width: 50
        color: "red"
        MouseRegion {
            anchors.fill: parent
            onClicked: {
                print("before append, size is" + rect.array.length);
                rect.array[rect.length] = null;
                print("after append, size is" + rect.array.length); //should be 1 more
            }
        }
    }
    Rectangle {
        x: 60
        height: 50
        width: 50
        color: "green"
        MouseRegion {
            anchors.fill: parent
            onClicked: {
                print("before append, size is" + rect.array.length);
                var arr = rect.array;
                arr[arr.length] = null;
                rect.array = arr;
                print("after append, size is" + rect.array.length); //should be 1 more
            }
        }
    }
}