MVC problem - view showing an old data

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C#

MVC

I have a simple View which updates a model:

@model FixPostWeb.Models.PostModel
....
@using (Html.BeginForm("Index", "FixPost",  FormMethod.Post))
{
 ... 
    <div class="update-field">
          @Html.TextAreaFor(model => model.OriginalPost)
    </div> 
    
    <div class="update-field">
          @Html.TextAreaFor(model => model.ConvertedPost)
    </div> 
}

In my controller I have a code:

public ActionResult FixPost(PostModel post)
{
....
    post.OriginalPost = "aaaaaaaaa";
    post.ConvertedPost = "aaaaaaaaa";
    return View(post);
...

But on return page the model.OriginalPost and the model.ConvertedPost show the value from the previous screen. I went through debugger and I am sure that "return View(post)" is executed where post.OriginalPost = "aaaaaaaaa"; and post.ConvertedPost = "aaaaaaaaa"; but instead values "aaaaaaaaa" it shows values from the previous screen.

Any ideas what I did wrong?

Thanks,

zalek