title: asp.net mvc ListBoxFor - MultiSelectList does not apply the selected item
body: <p>The tags are multi-selectable and are retrieved from the database.</p>
  
  <p>This is my action in the controller :</p>
  
  <pre><code>public ActionResult EditDocument(long documentId, string returnURL)
      {
          ViewBag.returnURL = returnURL;
  
          int userId = AccountController.GetLoggedInId(Session);
          string pageUrl = "Document/EditDocument";
  
          if (IsDocumentAccessible(documentId,pageUrl) &amp;&amp; CheckOperation("EditDocument",pageUrl))
          {
              try
              {
  
                  spGetDocumentById_Result found = db.spGetDocumentById(documentId).ToArray()[0];
  
                  EditDocumentViewModel model = new EditDocumentViewModel()
                  {
                      DocumentId = found.DocumentId,
                      DocumentNumber = found.DocumentNumber,
                      DocumentDate = found.DocumentDate,
                      DocumentLevelType = (int)found.DocumentLevelTypeId,
                      AddressSrc = found.Address
                  };
  
                  List&lt;spGetTagsOfDocument_Result&gt; tags = db.spGetTagsOfDocument(documentId).ToList();
  
                  foreach (spGetTagsOfDocument_Result tag in tags)
                  {
                      model.selectedTags.Add(tag.TagName);
                  }
  
                  List&lt;spGetAllDocumentLevelType_Result&gt; DocumentLevelTypeList = db.spGetAllDocumentLevelType(userId, pageUrl).ToList();
                  ViewBag.DocumentLevelTypeId = new SelectList(DocumentLevelTypeList, "DocumentLevelTypeId", "DocumentLevelTypeName");
  
                  List&lt;spGetAllTags_Result&gt; TagList = db.spGetAllTags(AccountController.GetLoggedInId(Session), "Document/AddDocument").ToList();
                  ViewBag.tags = new MultiSelectList(TagList, "TagId", "TagName", model.selectedTags.ToArray());
  
                  return View(model);
              }
              catch (Exception)
              {
                  return new HttpStatusCodeResult(HttpStatusCode.BadRequest);
              }
          }
  
          return new HttpStatusCodeResult(HttpStatusCode.Forbidden);
      }
  </code></pre>
  
  <p>and the view:</p>
  
  <pre><code>&lt;div class="form-group"&gt;
                              @Html.LabelFor(model =&gt; model.tags, new { @class = "col-sm-3 control-label" })
                              &lt;div class="col-sm-8"&gt;
                                  @Html.ListBoxFor(model =&gt; model.tags, ViewBag.tags as MultiSelectList, new { @class = "form-control" })
                              &lt;/div&gt;
                          &lt;/div&gt;
  </code></pre>
  
  <p>The thing is that the selected item does not apply!
  The multi-select element is filled fine but there is no preselection!</p>