When a sortable item is dragged, a placeholding <li> is added to the list to occupy dropping space. When the dragged <li> is dropped into this placeholding space the update callback is called before removing this temporary <li> element - any $('#_id_of_list > li') calls in this callback will return the correct <li> items plus the extra placeholding <li>. I've worked around this bug by adding a timeout inside the callback.