Sortable droppable mouse-detection problem

Sortable droppable mouse-detection problem


I use jQuery-ui to create a sortable list. Now, it's also droppable.
It is set correctly to my knowledge but it just won't detect any
draggables hovering or dropping onto them. What am I doing wrong? Has
it got something to do with the UL and LI being floated to the left?
File excerpts:
/*************************************************/
/* CSS
/*************************************************/
.sortableHover {
    background: #000;
}
div.emptyBlock {
    display: block;
    float: left;
    border: 1px solid #000;
    background: #fff;
    padding: .5em;
    margin: 2px .5em;
}
ul#import_order_ul {
    float: left;
    display: box;
    margin: .5em 0;
    padding: 0;
    border: 1px solid #666;
}
ul#import_order_ul li {
    display: block;
    float: left;
    border: 1px solid #000;
    background: #fff;
    padding: .5em;
    margin: 2px .5em;
}
/*************************************************/
/* JS
/*************************************************/
<script type="text/javascript">
    //<![CDATA[
    $(document).ready(function() {
        $(".emptyBlock").draggable({helper: "clone"});
        $("ul#import_order_ul").droppable({
            accept: ".emptyBlock",
            drop: function() {
                $(this).append("<li>*</li>");
            },
            hover: function() {
                alert("test");
            }
        }).sortable({
            hoverClass: "sortableHover",
            update: function() {
                var import_order = "";
                $("#import_order_ul").children().each(function() {
                    import_order = import_order + ";" + $(this).text();
                });
                $("#import_order").val(import_order);
            }
        });
    });
    //]]>
</script>
/*************************************************/
/* XHTML
/*************************************************/
<label for="import_order">Volgorde data:</label>
<input type="hidden" name="import_order" id="import_order"
value=";Voornaam;Tussenvoegsel;Achternaam;Klas;Cluster(s);Telefoonnummer;Leerlingnummer" /