MVC :: Model With List As Member: Member Always Null After Submit?

I have following model class:

public class WebModel
{
public List<ArticleModel> Articles { get; set; }
}
public class ArticleModel
{
public int ID { get; set; }
public double ValueParam { get; set; }
}

Then I have the controller with the two actions:

[Authorize]
public ActionResult Index()
{
WebModel model = new WebModel();
ModelConverter.ConvertToModel(model, controller);
return View(model);
}
[Authorize]
[HttpPost]
[ValidateInput(false)]
public ActionResult Index(WebModel model, string saveButton)
{
ModelValidation.ValidateWebModel(model, ModelState);
if (ModelState.IsValid)
{
return RedirectToAction("Create", "Article");
}
ModelConverter.ConvertToModel(model, controller);
return View(model);
}

And this is my view:

<%@ Page Title="" Language="C#" MasterPageFile="~/Views/Shared/Site.Master" Inherits="System.Web.Mvc.ViewPage<Web.Models.WebModel>" %>
<asp:Content ID="Content1" ContentPlaceHolderID="MainContent" runat="server">
<%var controller = Session["controller"] as Web.Code.SessionController; %>
<%Html.BeginForm(); %>
<div>
<table width="100%">
<%foreach (var article in Model.Articles)
{%>
<tr style="text-align: right">
<td>
<%:Html.DropDownListFor(m=>m.Articles.FirstOrDefault(f=>f.ID == article.ID).ID, new SelectList(controller.CurrentProdukt.Articles.AsEnumerable(), "ID", "Name", article.ID)) %>
</td>
<td>
<%:Html.TextBoxFor(m => m.Articles.FirstOrDefault(f => f.ID == article.ID).ValueParam)%>
</td>
</tr>
<%} %>
</table>
</div>
<table style="width: 100%">
<tr>
<td>
<input type="submit" name="saveButton" value="Save" />
</td>
</tr>
</table>
<%Html.EndForm(); %>
</asp:Content>

If I press the submit button, I get to the second action method in the controller (the one with the HttpPost attribute). In this action, the object model itself is not null, but the "Articles" list inside is null.