[jQuery] drag'n'drop, double added element

[quard]

Hello. I'm trying to create drag'n'drop interface with jQuery UI.

See code for adding to node.

$("#dropzone").droppable({
                        accept: '.imagethumb',
                        activeClass: 'droppable-active',
                        hoverClass: 'droppable-hover',
                        drop: function(ev, ui) {
                                var id = $(ui.draggable.element).attr("id");

                                var src = $("#" + id).find("img")[0];
                                src = $(src).attr("src");

                                var el = $("<img/>").attr("id", id +
"d").attr("src",src).addClass("draggable").draggable({revert: true});

                                $("#dropzone").append(el);
                        }
                });

If I drop element without FireBug checking and debugging,.I have two
element, (then 4, 6, 8, 10 and etc)

But if I create breakpoint and debug script only one element added.

Can't understand how it happens and what to do =(