C# - MVC - Blank Model Not Returning Blank Data

I have a form which a user can fill in x times with the data they want too. The form is posted to the following Action.

[HttpPost]
public ActionResult Manage(ProductOptionModel DataToAdd)
{
if (!ModelState.IsValid)
{
return View(DataToAdd);
}
var ProdServ = new ProductService();
if (DataToAdd.ID != 0)
{
//Edit Mode.
DataToAdd = ProdServ.EditProductOption(DataToAdd);
ViewData["Message"] = "Option Changes Made";
}else
{
//Add
DataToAdd = ProdServ.AddProductOption(DataToAdd);
ViewData["Message"] = "New Option Added";
}
var RetModel = new ProductOptionModel() {ProductID = DataToAdd.ProductID};
return View(RetModel);
}

So at the bottom I blank the model (Leaving just the required field) and then return to the view. However the view holds the data from the previously submitted form. I have debugged the code and checked that the RetModel variable is empty.