Dragging a item accross rows adds follow code between the rows:
<li class="item ui-sortable-placeholder" style="visibility: hidden; "></li>
But it doesn't move them after a drop and the list is not draggable after that anymore at all.
This seems to occur when you cross to a sublist.
Please see the short attached video showing this issue:
Issue solved, was my fault, due to faulty html.