MVC4 model changes not showing - asp.net-mvc-4

Question

I know what you're thinking, but hear me out.
I have a model:
public partial class DealerBudget
{
public int DealerBudgetID { get; set; }
public int DealerID { get; set; }
public int BudgetYr { get; set; }
public int BudgetMonth { get; set; }
public decimal BudgetAmt { get; set; }
public bool Confirmed { get; set; }
public short BudgetTypeID { get; set; }
}
A list of these is in a vm:
public class DealerBudgetVM
{
public List<CNHi.StMarys.ND.DBP.Web.Models.DealerBudget> YrBudget { get; set; }
}
They're filled in a Get:
public ActionResult Add()
{
DealerBudgetVM result = new DealerBudgetVM(); //initialised to have all 24 months
List<DealerBudget> dbList = db.DealerBudgets.Where(x => x.DealerID == dbp.dealerID && x.BudgetTypeID == (short)2 && (x.BudgetYr == DateTime.Now.Year || x.BudgetYr == DateTime.Now.Year + 1)).ToList();
//use the data from the DB if it exists
foreach (DealerBudget bud in result.YrBudget)
{
foreach (DealerBudget budDB in dbList)
{
bud.DealerID = dbp.dealerID;
bud.BudgetTypeID = 2; //Service
if (budDB.BudgetYr == bud.BudgetYr && budDB.BudgetMonth == bud.BudgetMonth)
{
bud.DealerBudgetID = budDB.DealerBudgetID;
bud.BudgetAmt = budDB.BudgetAmt;
bud.Confirmed = budDB.Confirmed;
}
}
}
return PartialView(result);
}
And displayed in a view. If each month's value is Confirmed, the textbox is disabled:
#for( int i = 0; i < 12; ++i)
{
#Html.HiddenFor(model => model.YrBudget[i].DealerBudgetID)
#Html.HiddenFor(model => model.YrBudget[i].BudgetTypeID)
#Html.HiddenFor(model => model.YrBudget[i].DealerID)
#Html.HiddenFor(model => model.YrBudget[i].BudgetYr)
#Html.HiddenFor(model => model.YrBudget[i].BudgetMonth)
#Html.HiddenFor(model => model.YrBudget[i].Confirmed)
<div class="pure-u-1-3 pure-u-md-1-6 pure-u-lg-1-12 s-box">
<span class="pure-u-1">#Html.DisplayFor(model => model.YrBudget[i].MonthDesc)</span>
#Html.TextBoxFor(model => model.YrBudget[i].BudgetAmt, (Model.YrBudget[i].Confirmed == false) ? (object)new {type="number", Value=Model.YrBudget[i].BudgetAmt.ToString("0.00")} : (object)new {disabled = "disabled", Value=Model.YrBudget[i].BudgetAmt.ToString("0.00")} )
</div>
}
The user enters new budget figures and saves:
[HttpPost]
public ActionResult Added(DealerBudgetVM vm)
{
if (ModelState.IsValid)
{
this.ModelState.Clear();
foreach (DealerBudget budVM in vm.YrBudget.Where(x => x.Confirmed == false && x.BudgetAmt > 0).ToList())
{
//If it's not in the DB, add it.
if (budVM.DealerBudgetID == 0)
{
DealerBudget budNew = new DealerBudget { BudgetYr = budVM.BudgetYr, DealerID = budVM.DealerID, BudgetMonth = budVM.BudgetMonth, BudgetTypeID = budVM.BudgetTypeID, BudgetAmt = budVM.BudgetAmt };
if (budNew.BudgetAmt > 0)
{
budNew.Confirmed = true;
budVM.Confirmed = true;
}
db.DealerBudgets.Add(budNew);
db.SaveChanges();
budVM.DealerBudgetID = budNew.DealerBudgetID;
}
else
{
//update and confirm
DealerBudget budDB = db.DealerBudgets.Where(x => x.DealerBudgetID == budVM.DealerBudgetID).FirstOrDefault();
if (budDB == null)
{
}
else
{
budDB.BudgetAmt = budVM.BudgetAmt;
budDB.Confirmed = true;
db.SaveChanges();
budVM.Confirmed = true;
}
}
}
return RedirectToAction("Index", "ServicePerformance");
}
else
{
return PartialView(vm);
}
}
...and nothing changes on the view. The new (confirmed) budget textboxes should be disabled, and they aren't.
"No problem!" you say. "this guy just needs to..."
Use ModelState.Clear(). Tried it, didn't work.
Remove keys from the ModelState. Tried it, didn't work.
Use Post-Redirect-Get. Tried it(both redirecting to the partial and to the master. Current code above still using it). Didn't work.
Clear the cache. Tried many, many methods and iterations. Nothing worked.
After the Post and save, the subsequent Get has all the correct saved values being sent to the View in the VM, but the old ones (ie user-entered values with confirmed flag=false) are still shown.
If the user then goes to another page and then returns, the page displays as expected.
All the posts I've seen here (and elsewhere) confidently declare that one of the four solutions above will fix it. I've wasted a day now banging my head against a wall trying to disable a stupid textbox.
Any other ideas? Is it because of nesting or partial views or something?