ASP.NET MVC 2.0: Making the POST Action receive my Model's sub-models

I'm trying to reuse some existing Models (and especially the Load/Save functions associated with them), so I've aggregated them into the current Model:

public class EditModel {
    public SubModel1 {get; set; }
    public SubModel2 {get; set; }
    /* ID and some text fields */
}

The problem is, after I fill the form and hit submit, in the Action associated with POST these sub-models all have default/empty content.

/// POST for Edit
    [OutputCache(NoStore = true, Duration = 0, VaryByParam = "*")]
    [AcceptVerbs(HttpVerbs.Post)]
    public ActionResult EditCommunity(EditCommunityModel model) {
        if (bad stuff happened)
            return Json("Failure");
        //model.SubModel1 is != null, but all fields are empty.
        // ID and the aforementioned text fields come correctly.
        Save(model.ID, model.SubModel1, model.SubModel2);
        return Json("Succeeded");
    }

I've done this reuse before without problems, when using an .aspx for the Edit equivalent, and would therefore call a GET Action to properly construct the Model. But now I'm restricted to an ascx, because I'm trying to edit in a modal dialog (if there's a way to load an aspx in a div, then this problem is over; but it occurs to me this would be contrary to what an aspx is intended for.)

This is, in short, what I'm trying to do; I'll also add two strategies I've tried to apply, both of which have the same effect: empty sub-models.

First try used an AJAX call to populate Edit.ascx. In Edit.ascx, the wrapper for edit dialog was included in Manage.aspx, and the EditModel was passed without any initialization

    <div id="editDialog" style="display: none;">
         <% Html.RenderPartial("Edit", new EditModel()); %>
    </div>

In the grid, a cell would be marked as edit, and on click would call the following javascript function:

    function onSelectRowEdit_Click(id) {
        if (id) {
            //Get data from selected row
            var ret = jQuery("#table_grid").getRowData(id);
            //Show Edit modal control
            var actionUrl = '<%= Url.Action("EditInfo", "Manage") %>';
            var data = "externalId=" + ret.OrgId + '&Id=' + ret.Id;
            $.ajax({
                type: "POST",
                url: actionUrl,
                data: data,
                error: AjaxError,
                success: ShowEdit
            });
     }
 }

EditInfo(string, string) would create and return a JsonResult, which was then received by ShowEdit; showEdit would fill Edit.ascx and use jQuery to present the div as a dialog:

    function ShowRes(ret) {
        $("#form_Edit").validate();
        jQuery("#editDialog").dialog('destroy');
        Init_EditDialog();

        /* $('#...').val(ret...);, many times over */

        //Show Dialog
        $("#editCommunityDialog_Content").show();
        $("#editCommunityDialog").dialog('open');
    }

Second try attempted to bypass new EditModel(), and to use a View returned by a Controller. It did achieve exactly what the first try did, with significantly less code, but had the same issue on Submit.

 <div id="editDialog" style="display: none;"></div>
 <!-- ... -->
 function onSelectRowEdit_Click(id) {
        if (id) {
            //Get data from selected row
            var ret = jQuery("#table_communities").getRowData(id);
            //Show Edit community modal control
            var actionUrl2 = '<%= Url.Action("ShowEdit", "Manage",
                new { CommunityId="_COMMID_", ExternalId="_ORGID_" }) %>';
            editImg = editImg.replace("_COMMID_", ret.Id);
            editImg = editImg.replace("_ORGID_", ret.OrgID);
            $.ajax({
                type: "POST",
                url: actionUrl2,
                data: data,
                error: AjaxError,
                success: ShowRes
            });
        }
    }

ShowEdit was rewritten to return View("Edit", model), and ShowRes would simply write the result to the div's html.

    function ShowRes(ret) {
        //...
        $("#editDialog_Content").html(ret);
        //Show Dialog
    }

Needless to say, the form in Edit.ascx has fields like <%= Html.HiddenFor(m => m.SubModel1.EditProfile)%> so that's not where the problem comes from.

Try checking out my answer in this question to see if that helps: How to handle `PartialRender` Models?