Telerik ComboBox Not binding on Second Click

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C#

ASP.NET

Telerik

Dear Developers,
i am binding comboBox in telerik, it binds well and while running the application it display the items bound on that combobox when user clicks first but when once he select any item and after that if he again click on the ComboBox it wont show all items rather its showing only the previous selected item.

My Code is-

<telerik:RadComboBox ID="rcbSearch" runat="server" CausesValidation="false"
            AutoPostBack="true" Width="160px"
            EmptyMessage="Select the Search Criteria" DropDownWidth="200px" HighlightTemplatedItems="true"
                            EnableLoadOnDemand="true"  Filter="StartsWith"
            OnItemsRequested="rcbSearch_ItemsRequested" Skin="Web20"
            onselectedindexchanged="rcbSearch_SelectedIndexChanged">
                            <HeaderTemplate>
                                <table style="width: 200px" cellspacing="0" cellpadding="0">
                                    <tr>
                                        <td align="left" style="width: 20px;">
                                            Code</td>
                                        <td align="left" style="width: 60px;">
                                            Description</td>
                                    </tr>
                                </table>
                            </HeaderTemplate>
                            <ItemTemplate>
                                <table style="width: 200px" cellspacing="0" cellpadding="0">
                                    <tr>
                                        <td align="left" style="width: 20px;">
                                            <%# DataBinder.Eval(Container, "Text")%>
                                        </td>
                                        <td align="left" style="width: 60px;">
                                            <%# DataBinder.Eval(Container, "Attributes['Description']")%>
                                        </td>
                                    </tr>
                                </table>
                            </ItemTemplate>
                        </telerik:RadComboBox>

Code Behind--

protected void rcbSearch_ItemsRequested(object sender, RadComboBoxItemsRequestedEventArgs e)
{
   fnbindComboBox();
}
#endregion
private void fnbindComboBox()
{
    DataTable dtTableDetails = new DataTable();
    _objAction = new DALSdfAction();
    dtTableDetails = _objAction.getTableDetails("sdfAction");

    foreach (DataRow dr in dtTableDetails.Rows)
    {
        RadComboBoxItem item = new RadComboBoxItem();
        item.Text = dr["sdfActionID"].ToString();
        string description = dr["dsc"].ToString();
        item.Attributes.Add("Description", description);
        rcbSearch.Items.Add(item);
        item.DataBind();
    }
}

Kindly help if you have some experience to Solve this issue.
Thanku.