ComboBox stops react on model change if empty list, null or undefined was set as model

import QtQuick 2.1
import QtQuick.Controls 1.0
import QtQuick.Layouts 1.0

GridLayout {
    property var originalModel: ["1", "2", "3", "4", "5"];

    property var undefinedModel: undefined;
    property var emptyModel: [];
    property var oneItemModel: ["0"];
    property var nullModel: null;

    function fill() {
        undefinedModel = originalModel;
        emptyModel = originalModel;
        oneItemModel = originalModel;
        nullModel = originalModel;
    }

    columns: 2

    Label { text: "original" }
    ComboBox { model: originalModel }

    Button {
        text: "fill"
        onClicked: fill()
        Layout.columnSpan: 2
    }

    Label { text: "undefined" }
    ComboBox { model: undefinedModel }

    Label { text: "empty" }
    ComboBox { model: emptyModel }

    Label { text: "oneItem" }
    ComboBox { model: oneItemModel }

    Label { text: "null" }
    ComboBox { model: nullModel }
}