IE7 and reverting draggables

IE7 and reverting draggables

Hi there.
I've got a page where you can drag a group of boxes around. Dropping them over a droppable div causes data to be entered into that div. I need to be able to get the data in multiple times, so I need to revert the boxes.
This works fine on FireFox, but on IE7 (and 8 and 6) you can only drag the boxes once, and then they won't go anywhere again.

Here is a page with the same problem taken down to it's simplest state: http://www.fullonrobotchubby.co.uk/random/drag_text.htm

The only jQuery code I have is the following:
$(document).ready(function(){
    $(".wave_holder").Draggable({
        revert: true
    });

    $(".has_received").Droppable({
        accept : 'wave_holder',
        tolerance: 'pointer'     
    });
});


What am I doing wrong?