ASP.NET Razor ViewModel property is modified somewhere - asp.net

Question

I have an extremely simple Controller + View
public ActionResult Edit(string username)
{
return View(ComponentFactory.GetAdapter<IUserListAdapter>().Get(username));
}
and
#model BAP.Models.UserList
#using GrmanIT.Utils.Web
#using BAP.Models
#using (Html.BeginForm())
{
#Html.AntiForgeryToken()
#Html.ValidationSummary(true)
<fieldset>
<legend>Globale Benutzer</legend>
<div class="editor-label">
#Html.LabelFor(model => model.UserId)
</div>
<div class="editor-field">
#Html.EditorFor(model => model.UserId)
#Html.ValidationMessageFor(model => model.UserId)
</div>
<div class="editor-label">
#Html.LabelFor(model => model.UserName)
</div>
<div class="editor-field">
#Html.EditorFor(model => model.UserName)
#Model.UserName
#Html.ValidationMessageFor(model => model.UserName)
</div>
<div class="editor-label">
#Html.LabelFor(model => model.Bundesland)
</div>
<div class="editor-field">
#Html.DropDownListFor(model => model.Bundesland, new SelectList((IEnumerable<BAP.Models.Bundesland>)ViewData["BundeslandList"], "Value", "Text"))
</div>
<div>
<input type="submit" value="#LocalizationHelper.LocalizedLiteral("Save").ToString()" />
</div>
</fieldset>
}
<div>
#Html.ActionLink(LocalizationHelper.LocalizedLiteral("BackToList").ToString(), "Index")
</div>
#Model.UserName
this is by far the simplest controller and view we have in our MVC4 application, BUT - it does something weird:
I get the TextBox, which is created with #Html.EditorFor(model => model.UserName) prefilled with the UserId of the model instead of the UserName
I debugged it and it and there as always the correct value in UserName and UserId. You can also see, that I added #Model.UserName twice within the View to see if it get also correctly rendered, and yes, it prints the UserName and not the ID.
I've also checked references to the UserName-property and didn't find any, which would modify it. My question is - do you have any idea, where the code could be modified or how could if find it out?
It happens only on this one controller on this one action (out of ~25 controllers and ~200 actions)
Thank you

Answer 1

Ok, it was AGAIN the ModelState - as you can see in the code above - the parameter to the function is called "username" but it's actually the userId. And since there is already the parameter username, it is stored in the ModelState and when I call
#Html.EditorFor(model => model.UserName)
it takes the value from the ModelState (where actually the UserId is stored under the name of the action-parameter)
So the solution would be, either to call ModelState.Clear() or rather, rename the parameter to represent the actual value.