div tag breaks jqxTree

Demonstrates that an addition div tag when a jqxTree is present causes tree not to render.

HTML

<link rel="stylesheet" href="https://jqwidgets.com/public/jqwidgets/styles/jqx.base.css">
<link rel="stylesheet" href="https://jqwidgets.com/public/jqwidgets/styles/jqx.energyblue.css">
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.2/jquery.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/3.6.0/lodash.min.js"></script>
<script src="https://jqwidgets.com/public/jqwidgets/jqx-all.js"></script>
<div id='jqxWindow'>
    <div id='jqxTree'></div>
    <p>This is some text</p>
    <!-- Remove this line to show problem
        <div></div>
    Remove this line to show problem -->
</div>

JavaScript

var source = [{
    label: "Mail"
}, {
    label: "Inbox"
}, {
    label: "Deleted Items"
}, {
    label: "Notes"
}, {
    label: "Settings"
}, {
    label: "Favorites"
} ];

$('#jqxWindow').jqxWindow({
    theme: 'energyblue',
    width: '200px',
    height: '400px',
    isModal: true,
    autoOpen: true,
    resizable: false,
    title: 'This is a jqxWindow'
});

$('#jqxTree').jqxTree({
    source: source,
    width: '200px',
    height: '200px',
    theme: 'energyblue'
});