.NET MVC+extjs中关于在调试时grid数据显示不出来

这些代码我在VS2013中右键浏览页面数据都是可以正常显示的，可是按F5调试的时候数据就显示不出来这是为什么呢？

后台Controller中action代码：

 public ActionResult Getinfo(){
var list = new List<UserStore>();
list.Add(new UserStore() { EmailAddress = "r.taylor@abc.com", FirstName = "Rose", LastName = "Taylor" });
list.Add(new UserStore() { EmailAddress = "r.Nguyen@abc.com", FirstName = "Russell", LastName = "Nguyen" });
return Content(JsonConvert.SerializeObject(list)); 
}

ext示例代码：

 Ext.define('UserList', {
    extend: 'Ext.data.Model',
    fields: ['firstName', 'lastName', 'emailAddress'] //you can comment these fields. It still works.  
});

var userStore = Ext.create('Ext.data.Store', {
    model: 'UserList',
    proxy: {
        type: 'ajax',
        url: 'Getinfo',
        actionMethods: {
            read: 'POST' // Store设置请求的方法，与Ajax请求有区别  
        },
        reader: {
            totalProperty: 'totalCount',
            root: 'roots'
        }
    }
});
userStore.load();
//定义分页    
var pagebar = Ext.create("Ext.toolbar.Paging", {
    store: userStore,
    displayInfo: true,
    displayMsg: "显示{0}-{1}条,共计{2}条",
    emptyMsg: "没有数据"

});

Ext.application({
    name: 'Ext6 Grid示例',
    launch: function () {
        Ext.create('Ext.grid.Panel', {
            renderTo: Ext.getBody(),
            selType: 'rowmodel',//'cellmodel',  
            plugins: [{
                ptype: 'rowediting',
                clicksToEdit: 1
            }],
            store: userStore,
            columnLines: true,
            //width: "100%",  
            //frame: true,  
            forceFit: true,
            fixed: true,
            height: 500,
            title: 'Ext6 Grid示例',

            columns: [
                 {
                     text: 'First Name',
                     width: 200,
                     dataIndex: 'FirstName',
                     editor: 'textfield'
                 },
                 {
                     text: 'Last Name',
                     width: 200,
                     dataIndex: 'LastName',
                     editor: 'textfield'
                 },
                 {
                     text: 'Email Address',
                     width: 250,
                     dataIndex: 'EmailAddress',
                     editor: {
                         xtype: 'textfield',
                         allowBlank: false
                     }
                 },
                  {
                      text: 'Birth Date',
                      width: 250,
                      dataIndex: 'birthDate',
                      editor: 'datefield'
                  }
            ],
            //分页功能  
            //bbar: pagebar,  
            //分页功能-效果同上      
            dockedItems: [{
                xtype: 'pagingtoolbar',
                store: userStore,
                dock: 'bottom',
                displayInfo: true,
            }]
        });

    }
});

重点就在于我右键index.cshtml->浏览方式->选择ie的时候。整个grid数据都是能够正常加载的。按f5调试时只能显示grid而数据就死活出不来，我能肯定数据是有返回到页面的。
因为在不用ext的情况下，我让后台直接数据直接返回在页面上，返回的数据是对的。

[{"FirstName":"Rose","LastName":"Taylor","EmailAddress":"r.taylor@abc.com"},{"FirstName":"Russell","LastName":"Nguyen","EmailAddress":"r.Nguyen@abc.com"},{"FirstName":"Ellis","LastName":"Davis","EmailAddress":"e.davis@abc.com"},{"FirstName":"Neal","LastName":"Clarke","EmailAddress":"n.clarke@abc.com"},{"FirstName":"Brendon","LastName":"Taylor","EmailAddress":"b.taylor@abc.com"}]
这是直接返回在页面上的数据及格式

怎么没有birthDate？

这是右键浏览时，数据正常的界面

这是按F5调试时，数据出不来的界面，两者代码没有变动
请教一下这里的大神