If you want to use a callback function when the sort stop/update this callback function is called before the sort stop.

So you have a "ghost" of the element you want to move.

In my case i sort div elements that contains hidden input.

You can use this callback function to show the problem :

fonction(e, ui){
    $('div.sortable input[class="order"]').each(function(i){
            alert($(this).attr('name'));
        }
    )
}

however if you use console.log whith firebug you will not see this "ghost" element