jQuery mouseleave not firing correctly while dragging

I have a sortable list with a mouseleave event listener that is behaving incorrectly.

If I move the mouse in and out of the sortable list, mouseleave fires correctly.

If I first click and drag one of the sortable's children, mouseleave fires incorrectly - sporadically or not at all.

Any ideas?

Thanks.

update: This occurs for mouseout events as well.

<style>
#sortable { list-style-type: none; margin: 0; padding: 0; float: left; margin-right: 10px; background-color: #CCC; }

#sortable li { margin: 0 5px 5px 5px; padding: 5px; font-size: 1.2em; width: 120px; }
</style>

<script>
  $(function(){
    $("#sortable").sortable().disableSelection();
    $("#sortable").mouseleave(function(){ console.log("mouseleave"); });
  });   
</script>

<ul id="sortable">
  <li class="ui-state-default">Item 1</li>
  <li class="ui-state-default">Item 2</li>
  <li class="ui-state-default">Item 3</li>
</ul>

update I have used the following to detect when a child has been dragged fully outside of the sortable:

$("#sortable li").mousemove(function() {
        if ($(this).offset().left > $(this).parent().outerWidth() + $(this).parent().offset().left ||
                $(this).offset().top > $(this).parent().outerHeight() + $(this).parent().offset().top  ||
                $(this).offset().left + $(this).outerWidth() < $(this).parent().offset().left  ||
                $(this).offset().top + $(this).outerHeight() < $(this).parent().offset().top ){
                console.log("child is outside parent");
            }
    });