listview, datapager, objectdatasource not working in updatepanel
===

When i change the page in datapager it causes full postback, even the datapager is working very abnormally, idont know what is the reason. by abnormaaly i mean sometime data is shown sometime doesnt,    
Following is th my code in c#    

    	 protected void Page_Load(object sender, EventArgs e)
        {
            if (!IsPostBack)
            {
                BindListView();
            }           
        }

        protected void StudentListView_PagePropertiesChanging(object sender, PagePropertiesChangingEventArgs e)
        {
            BindListView();
        }
        private void BindListView()
        {
            StudentListView.DataSource = StudentDataSource;
            StudentListView.DataBind();
        }

        protected void StudentDataSource_Selecting(object sender, ObjectDataSourceSelectingEventArgs e)
        {
            e.Arguments.MaximumRows = StudentListDataPager.MaximumRows;
            e.Arguments.StartRowIndex = StudentListDataPager.StartRowIndex;
        }

Following is my markup      

        <asp:UpdatePanel runat="server" UpdateMode="Conditional">
        <ContentTemplate>        <
        <asp:DropDownList runat="server" ID="BatchDropDownList" AutoPostBack="True">
            <asp:ListItem Text="Batch 1" Value="1" Selected="True" />
            <asp:ListItem Text="Batch 2" Value="2" />
        </asp:DropDownList>

        <asp:ListView ID="StudentListView" runat="server"       
            ItemPlaceholderID="ListViewContent" 
                EnableViewState="false" 
                onpagepropertieschanging="StudentListView_PagePropertiesChanging"> 
            <LayoutTemplate> 
                <table style="width:100%">
                    <thead>
                        <tr>
                            <th class="align-left"><strong>Name</strong></th>
                            <th class="align-left"><strong>MobNo</strong></th>
                        </tr>
                    </thead>
                    <tbody runat="server" id="ListViewContent"> 
                    </tbody>
                    <tfoot>
                        <tr>
                            <td colspan="3">
                                
                            </td>
                        </tr>
                    </tfoot>
                </table>
                
            </LayoutTemplate>  
            <ItemTemplate>  
                
                <tr>
                    <td style="width:70%;"><%# Eval("FirstName") %>&nbsp<%# Eval("LastName") %></td>
                    <td style="width:30%;"><%# Eval("MobNo") %></td>                    
                </tr>

            </ItemTemplate>             
        </asp:ListView>
        <asp:DataPager ID="StudentListDataPager" runat="server" PageSize="5" PagedControlID="StudentListView">
            <Fields>
                <asp:NumericPagerField />
            </Fields>
        </asp:DataPager>
        

        <asp:ObjectDataSource ID="StudentDataSource" runat="server" 
            SelectMethod="GetStudentListBatchWise" SelectCountMethod="StudentCount" 
                TypeName="SCERPCommonUtil.Student" EnablePaging="True" 
                onselecting="StudentDataSource_Selecting">
            <SelectParameters>
                <asp:ControlParameter Name="batchId" ControlID="BatchDropDownList" PropertyName="SelectedValue" />
            </SelectParameters>
        </asp:ObjectDataSource>
        </ContentTemplate>
    </asp:UpdatePanel>
Please tell me if i am making any mistakes.    

P.S. : Please dont point me to any stackoverflow question as i have read all of them, and none is specific to my requirement,