问ASP.Net MVC AJAX上传文件被提交给控制器两次

EN

@using (Ajax.BeginForm("Create", "MyController", new { area = "" },
    new AjaxOptions
    {
        HttpMethod = "POST",
        OnBegin = "onBegin",
        OnSuccess = "onSuccess(data)"
    }, new { enctype = "multipart/form-data", id = "myform" }))
    {

    <section class="col col-md-12">
        @Html.DisplayFor(model => model.Title)
        <label class="input">
            @Html.TextBoxFor(model => model.Title)
        </label>
    </section>

    <section class="col-md-6">
        <label class="label text-left">
            My File
        </label>
        <label for="file" class="input input-file">
            <div class="button">
                <input name="files" type="file" id="file" onchange=" this.parentNode.nextSibling.value = this.value ">choose...
            </div>
            <input type="text" readonly="" class="text-right">
        </label>
    </section>

    <button type="submit" class="btn btn-primary">
        Submit
    </button>
}

[HttpPost]
public ActionResult Create(HttpPostedFileBase files, CreateViewModel model)
{
    // The Request comes here twice.
}

<script src="/Scripts/jquery.min.js"></script>
<script src="/Scripts/jquery.unobtrusive-ajax.min.js"></script>
<script src="/Scripts/jquery.validate.min.js"></script>
<script src="/Scripts/jquery.validate.unobtrusive.min.js"></script>
<script src="/Scripts/bootstrap/bootstrap.min.js"></script>
<script src="/Scripts/jquery.form.js"></script>

$(function () {
    $('#myform').ajaxForm({
        beforeSubmit: ShowRequest,
        success: SubmitSuccesful,
        error: AjaxError
    });
});

function ShowRequest(formData, jqForm, options) {
    var queryString = $.param(formData);

    alert('BeforeSend method: \n\nAbout to submit: \n\n' + queryString);
    return true;
}

function AjaxError() {
    alert("An AJAX error occured.");
}

function SubmitSuccesful(responseText, statusText) {
    alert("SuccesMethod:\n\n" + responseText);
}