$('.draggable').draggable({
  revert: "invalid",
  stack: ".draggable",
  helper: 'clone'
});
$('.droppable').droppable({
  accept: ".draggable",
  drop: function(event, ui) {
    var droppable = $(this);
    var draggable = ui.draggable;
    // Move draggable into droppable
    var drag = $('.droppable').has(ui.draggable).length ? draggable : draggable.clone().draggable({
      revert: "invalid",
      stack: ".draggable",
      helper: 'clone'
    });
    drag.appendTo(droppable);
    draggable.css({
      float: 'left'
    });
  }
});