open a modal dialog inside another modal dialog

i'm using JQuery v2.1.1 and JQuery UI v1.11.0, i'm trying to open a modal dialog inside another one, with the first (parent) dialog disabled as the background.

In both dialog the modal properties is true, but only the background in disabled, not the first dialog.

This is the HTML:

<div id="dialog-first" title="1st Modal">
    First Modal
    <input type="text" id="onetext"/>
</div>

<div id="dialog-second" title="2nd Modal">
    Second Modal
</div>

And the JS:

$( "#dialog-first" ).dialog({
    height: 300,
    modal: true,
    buttons: {
        Cancel: function() {
            $(this).dialog('close');
        }
    }
});

$( "#dialog-second" ).dialog({
    autoOpen: false,
    modal: true,
    buttons: {
        Cancel: function() {
            $(this).dialog('close');
        }
    }
});

$("#onetext").dblclick(function() {
    $("#dialog-second").dialog("open");
});

For test, i wrote the code at: http://jsfiddle.net/33PQj/