第一次双击按钮的时候，追加的文本框出现了，再次双击的时候，又消失了， 这是为什么呢？

@model Vote.Models.

 VoteDetailModel

@{

ViewBag.Title =

 "VoteUpdate";

}

<h2>Vote Update</h2>

@section BodyEnd{

<scriptsrc="../../Scripts/jquery-2.1.0.js"type="text/javascript"></script>

<scripttype="text/javascript">

        $(document).ready(

function () {           

var fieldCount = 1;

            $('#btnAddItem').click(function (e) { 

var $div = $('<div/>');            

var $newInput = $('<input/>', {

                    type:'text',

                    id:'txt_' + fieldCount

                });

                $('#addItems').append($div).append($newInput);

                fieldCount++;

            });

        });

</script>

}

@*

@Html.TextBoxFor(m => m.VoteItems[0])@Html.ValidationMessageFor(m => m.VoteItems[0])*@

@

 using (Html.BeginForm()){@Html.ValidationSummary(true, "Account creation was unsuccessful. Please correct the errors and try again.")

<div>

<fieldset> 

<legend>Update Vote Items</legend>      

<divclass="editor-label">

                @Html.LabelFor(m => m.VoteTitle)

</div>

<divclass="editor-field">

                @Html.TextBoxFor(m => m.VoteTitle)

                @Html.ValidationMessageFor(m => m.VoteTitle)

</div>  

<divclass="editor-label">

                @Html.LabelFor(m => m.VoteItems)

</div>   

<divid="addItems">       

<div>    

<inputid="txt_0"type="text"/>    

</div>      

</div>    

<inputid="btnAddItem"type="submit"value="+"/>        

<p>             

<inputtype="submit"value="Save"/>       

</p>

</fieldset>

</div>

}