Custom sSortDataType

Hello,

I'm facing a problem with custom sorting datas
My test page is available here http://www.strangeplanet.fr/files/movies.htm

For "Name" and "Filesize" collumns I added a "data-value" attribute with different data than displayed :
for filesizes I use the complete value in bytes and for names I "overwrite" articles ("The Aviator" becomes "A. The Aviator") in order to have kind of natural sorting

then I use this SortDataType (adapted from the doc)

jQuery.extend( jQuery.fn.dataTableExt.afnSortData, {
    'data-value': function ( oSettings, iColumn ) {
        var aData = [];
        $( 'td:eq('+iColumn+')', oSettings.oApi._fnGetTrNodes(oSettings) ).each( function () {
            aData.push( $(this).data('value') );
        } );
        return aData;
    }
});

var oTable = $('#list').dataTable({
    "bJQueryUI": true,
    "aaSorting": [ [0,'asc'] ],
    "aoColumns": [
          { "sSortDataType": "data-value", "sType": "natural" },
          { "sType": "720-1080" },
          null,
          { "sSortDataType": "data-value", "sType": "numeric" },
          { "sType": "date-uk" }
    ]
});

my problem is that... it doesn't work ! the initial sorting on "Name" collumn is good, but if I change it, things are messed up (names begining with a figure are not at the begining of the table). it's way more visible on the "Filesize" collumn, first time you have a nice order from 384 Mio to 20Gio and then..... nothing

what am I doing wrong ?

Thanks