JQuery 1.5a demo bug - sortable boxes

Sometimes when holding the dragged item over another item, where one
would expect the existing item to move out the way so that the dragged
item can be placed there, but it doesn't - instead the one on the left
does.
Please view screencast of problem below (packaged as SWF file):
http://s000.tinyupload.com/index.php?file_id=64815297263102679018