In Asp.Net MVC view dont render changes in model made by controller

Question

Im new to ASP.NET MVC and need some help.
When "P01" action is fired by post i receive the strongly typed model as parameter, change properties of this model instance and call "return View(model);".
In view im using "@Html.TextBoxFor(m => m.p01campo01)" syntax.
Someone here had a similar problem and get advice to use the syntax im using.
Someone here is using "<%=Html.TextBox("Person.LastName", ViewData.Model.LastName)%>" syntax.
The problem is when the view is rendered the textbox have the last posted value, not the value i assigned in controller.

Thanks for everyone that have tried to help me here, i put as answer the first answer that work.

There is my code:

*************************************************
using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.Globalization;
using System.Linq;
using System.Web;
using System.Web.Mvc;
using System.Web.Security;

namespace MyTest.Models
{
    //-------
    public class testePg01
    {        
        [DataType(DataType.Text)]
        [Display(Name = "p01campo01")]
        public string p01campo01 { get; set; }

        [DataType(DataType.Text)]
        [Display(Name = "p01campo02")]
        public string p01campo02 { get; set; }

    }
    //-------
}
*************************************************

*************************************************
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Mvc;
using MyTest.Models;

namespace MyTest.Controllers
{
    public class TesteController : Controller
    {
        //-------
        [AcceptVerbs(HttpVerbs.Get)]        
        public ActionResult P01()
        {
            return View();
        }
        //-------
        [AcceptVerbs(HttpVerbs.Post)]
        [ValidateAntiForgeryToken]
        public ActionResult P01(testePg01 model)
        {
            model.p01campo01 = model.p01campo01 + "#updatedHereButNotInView";
            model.p01campo02 = model.p01campo02 + "#updatedHereButNotInView";
            return View(model); // it dont return updated
        }
        //-------

    }
}
*************************************************

*************************************************
@model MyTest.Models.testePg01

@{
    ViewBag.Title = "P01";
}

<h2>P01</h2>

<script src="@Url.Content("~/Scripts/jquery.validate.min.js")" type="text/javascript"></script>
<script src="@Url.Content("~/Scripts/jquery.validate.unobtrusive.min.js")" type="text/javascript"></script>

@Html.ValidationSummary(true, "Erro na pagina.")

@using (Html.BeginForm()) {
    @Html.AntiForgeryToken()
    <div>    
        <fieldset>
            <legend>Test P01</legend>

            <div class="editor-label">
                @Html.LabelFor(m => m.p01campo01)
            </div>
            <div class="editor-field">
                @Html.TextBoxFor(m => m.p01campo01)
                @Html.ValidationMessageFor(m => m.p01campo01)
            </div>

            <div class="editor-label">
                @Html.LabelFor(m => m.p01campo02)
            </div>
            <div class="editor-field">
                @Html.TextBoxFor(m => m.p01campo02)
                @Html.ValidationMessageFor(m => m.p01campo02)
            </div>
            <p>
                <input type="submit" value="P01" />
            </p>
        </fieldset>
    </div>
}
*************************************************

Answer 1

Model changes made in a post are not rendered by default. Instead it uses what was passed in the model to the controller method. To fix this, try adding:

ModelState.Clear();

immediately before the RedirectToAction.