autocomplete is firing when ctrl or alt key is pressed

autocomplete is firing when ctrl or alt key is pressed

hi there,
I have a strange problem , i am using jquery ui autocomplete. After the selection from the result returned. if user press ctrl key or alt key(and some other keys) its sending call to server. what is this?? here is my code. secondly how to handle if no data is returned from the server. here is how i am using.

  1. $(function() {
               var selecationMade = false;
               var local = {};
               $("#txt").autocomplete({
               minLength: 3,
               delay: 100,
               search: function(event,ui){ selecationMade = false;},
               source:function(request, response) {
                        $.ajax({
                            url: "/httphandlers/SearchLocationContents.ashx",
                            data: "term=" + request.term,
                            dataType: "json",
                            type: "Get",
                            contentType: "application/jsonp; charset=utf-8",
                            success: function(data) {
                                response(data);
                            },
                            complete: function(jqXHR, textStatus) {
                                local = $.parseJSON(jqXHR.responseText);
                            },
                            error: function(jqXHR, textStatus, errorThrown){alert(errorThrown);}
                        });
                    },
               select:function(event,ui){selecationMade = true;}
               });
                $("#txt").blur(function(){
                if(!selecationMade)// if user move without selecting , select the first item
                {
                    $("#txt").val(local[0].value);
                }
               });
            });