[jQuery] problem with click event-IE needs to click where FF needs only one:

[jQuery] problem with click event-IE needs to click where FF needs only one:

<script type="text/javascript">
    $(document).ready(function(){
    $("#pac").click(function(){
    $("#pac").animate({marginTop: "17px", paddingBottom: "17px",
borderBottom: "2px solid white"}, 2500 );
    $.post("rpc.php", {u:"genia"}, function(data){
         if(data.length >0) {
$("#pac_c").append(data);
     }else{
            $("#pac_c").css({overflow: "none", display: "none"});
            }
        $("#pac_c").css({overflow: "auto", display: "block"});
})});
    });
</script>
In FF the div animates and do the Post with only one click(like i
want) on IE i need to click twice for it to the POST too/
any help?