Sortable does not scroll

Sortable does not scroll

I have a similar import code:

<script type="text/javascript" src="jquery/jquery-1.4.2.min.js"></script>

<script type="text/javascript" src="jquery/ui/jquery.ui.core.js"></script>
<script type="text/javascript" src="jquery/ui/jquery.ui.widget.js"></script>
<script type="text/javascript" src="jquery/ui/jquery.ui.mouse.js"></script>
<script type="text/javascript" src="jquery/ui/jquery.ui.draggable.js"></script>
<script type="text/javascript" src="jquery/ui/jquery.ui.resizable.js"></script>
<script type="text/javascript" src="jquery/ui/jquery.ui.sortable.js"></script>

and this javascript code:

$(document).ready(function() {
        $("##listacolori").sortable({
            opacity: .5,
            placeholder: "placeholder",
            cursor: "move",
            axis: 'y',
            update: function(event, ui) {
                var colori = $(this).sortable('toArray').toString();
                $("##ajxResult").html('Attendere prego...');
                $.post("include/xxx/xxx.cfm",{
                    colorList:             colori,
                    codice_occhiale:    "#qryColori.codice#"
                },
                function() { $("##ajxResult").html('Ordinamento colori aggiornato!'); });
            }
        });
      });

Here's some of my CSS:
<style type="text/css">
.column {
    float:left;
    margin-right:10px;
}
ul {
    padding:0;   
    list-style:none;
}
li.cell {
    height:60px;
    margin:5px 0px 5px 0px;
    padding:5px 0px 0px 5px;
    border:1px solid #EDF0F4;
}
#listacolori li {
    border:1px solid #444;
    background-color:#FFF;
    -moz-border-radius:10px;
    width:400px;
}
.placeholder {
    height:60px;
    margin:5px 0px 5px 0px;
    padding:5px 0px 0px 5px;
    border:1px solid #EDF0F4;
    background-color:#FFC;   
    -moz-border-radius:10px;
    width:400px;
}
</style>

In my layout there's a column containing the sortable list. In the end a clear:both.
All works fine.
But... auto-scrolling of pages doesn't work. Dragging to the bottom a <li> doesn't make page scroll down.

What can cause non-scrolling of the page in presence of a sortable/draggable?
What can I check?

Thanks a lot everyone!