Number <input> value restored when opening dialog

HTML

<link rel="stylesheet" href="http://ajax.googleapis.com/ajax/libs/jqueryui/1/themes/base/jquery-ui.css">
<div class="dialog">
    <input id="num" type="number" value="123">
    <input id="text" type="text" value="456">
</div>

JavaScript

$('.dialog').dialog();

function log(message) {
    $('body').append(
        '<p>'
        + message + ': '
        + $('#num').val() + '/' + $('#text').val()
        + '</p>'
    );
}

$('.dialog').dialog('close');
log('Before clearing value (expected 123/456)');

$('input').val('');
log('Before opening dialog (expected both empty)');

$('.dialog').dialog('open');
log('After opening dialog (expected both empty)');