title: Update Panel and Dropdown Selected Index change Issue
body: <p>I have two dropdowns categories and subcategories on my page. Also I have an htmleditor on the same page. Below is my aspx</p>
  
  <pre><code>&lt;div class="clearfx"&gt;
      &lt;/div&gt;
       &lt;div&gt;
           &lt;label&gt;
               Description :
                  &lt;/label&gt;
                   &lt;div style="padding-left: 10px; margin-left: 146px;"&gt;
                      &lt;cc:HtmlEditor ID="Editor" runat="server" Height="600px" Width="850px" EnableViewState="true" /&gt;
                              &lt;/div&gt;
                          &lt;/div&gt;
                          &lt;div class="clearfx"&gt;
                          &lt;/div&gt;
                          &lt;div&gt;
                              &lt;asp:UpdatePanel runat="server" ID="up" UpdateMode="Always" ChildrenAsTriggers="true"&gt;
                                  &lt;ContentTemplate&gt;
                                      &lt;label&gt;Category : &lt;/label&gt;
                                      &lt;asp:DropDownList runat="server" ID="Categories" Width="200px" AutoPostBack="True"
                                          OnSelectedIndexChanged="CategoriesSelectedIndexChanged"&gt;
                                      &lt;/asp:DropDownList&gt;
                                     &lt;asp:RequiredFieldValidator ID="rfvCountry" runat="server" ErrorMessage="Choose a category."
                                          ControlToValidate="Categories" Display="None" EnableTheming="False" EnableViewState="False"
                                          InitialValue="-1" SetFocusOnError="True" ValidationGroup="grpReg"&gt;&lt;/asp:RequiredFieldValidator&gt;
                                      &lt;asp:ValidatorCalloutExtender ID="rfvCountry_ValidatorCalloutExtender" runat="server"
                                          Enabled="True" TargetControlID="rfvCountry"&gt;
                                      &lt;/asp:ValidatorCalloutExtender&gt;
                                       &lt;asp:ImageButton runat="server" ID="Refresh" ImageAlign="AbsMiddle" 
                                          ImageUrl="~/cdn/images/refresh.png" onclick="RefreshClick"/&gt; 
                                           &lt;span class="helptext"&gt;(click on refresh image, incase subcategories do not load.)&lt;/span&gt;
                                  &lt;/ContentTemplate&gt;
  
                              &lt;/asp:UpdatePanel&gt;
  
                          &lt;/div&gt;
                          &lt;div class="clearfx"&gt;
                          &lt;/div&gt;
  
  &lt;div&gt;
                              &lt;label&gt;
                                  Sub Category :
                              &lt;/label&gt;
                              &lt;asp:DropDownList runat="server" ID="SubCategories"  Width="200px"&gt;
                              &lt;/asp:DropDownList&gt;
                              &lt;asp:RequiredFieldValidator ID="RequiredFieldValidator2" runat="server" ErrorMessage="Choose a sub category."
                                  ControlToValidate="SubCategories" Display="None" EnableTheming="False" EnableViewState="False"
                                  InitialValue="-1" SetFocusOnError="True" ValidationGroup="grpReg"&gt;&lt;/asp:RequiredFieldValidator&gt;
                              &lt;asp:ValidatorCalloutExtender ID="ValidatorCalloutExtender2" runat="server" Enabled="True"
                                  TargetControlID="RequiredFieldValidator2"&gt;
                              &lt;/asp:ValidatorCalloutExtender&gt;
                          &lt;/div&gt;
  </code></pre>
  
  <p>What I am doing is that, On the selected index change of the categories dropdown i am populating subcategories.  to suppress post back i am using an Update Panel, But my problem is that,the selected index change is fired but the dropdown subcategories does not gets binded. When I remove the update panel, then its works fine, but my html editor looses its value, even having its own and Page enableviewstate = true. Please help me.</p>
  
  <p>My Codebehind methods are:
  Dropdown Selected Index Change Event:</p>
  
  <pre><code>protected void CategoriesSelectedIndexChanged(object sender, EventArgs e)
          {
              if (Categories.SelectedIndex &gt; 0)
              {
                  BindSubCategory(Common.ParseInt(Categories.SelectedItem.Value));
              }
              else
              {
                  SubCategories.SelectedIndex = 0;
                  SubCategories.Items.Clear();
              }
          } 
  </code></pre>
  
  <p>Page Load Event:</p>
  
  <pre><code> protected void Page_Load(object sender, EventArgs e)
          {
              if (!IsPostBack)
              {
                  BindGrid();
                  BindCategories();
              }
          }
  
   private void BindCategories()
          {
              List&lt;Category&gt; cat = _categoryRepository.GetAll().ToList();
              Common.BindDropdown(cat, Categories); // static method
          }
   public static class Common
      {
   /// &lt;summary&gt;
          /// 
          /// &lt;/summary&gt;
          /// &lt;param name="list"&gt;&lt;/param&gt;
          /// &lt;param name="ddl"&gt;&lt;/param&gt;
          public static void BindDropdown(IList list, DropDownList ddl)
          {
              if (list.Count&gt;0)
              {
  
  
                      ddl.DataSource = list;
                      ddl.DataTextField = "Name";
                      ddl.DataValueField = "Id";
                      ddl.DataBind();
                      ddl.Items.Insert(0, new ListItem("---Select---", "-1"));
  
              }
          }
  }
  </code></pre>