MVC 3 The View is not being refreshed after model submit

You need to remove the value from the ModelState if you want to modify it in a post/get:

[HttpPost]
public ViewResult EditUserData(UserData model)
{
    ModelState.Remove("Name");
    model.Name = "ipsum";
    return View("~/Views/UserDetails.cshtml", model);    
}

This is the built in MVC behavoir: all the Html.Helpers prefers the values in the ModelState collection over the actual model values.

There is a good article about this here: ASP.NET MVC Postbacks and HtmlHelper Controls ignoring Model Changes.

This is by design. MVC is assuming that you want to show what the user initially submitted when processing a post action. See this related stack overflow post.