Asp.net gridview template field irrelevant behaviour

<asp:GridView ID="gdvAssetType" runat ="server" AllowPaging="True"
                               AutoGenerateColumns="False" BackColor="White" BorderColor="#CCCCCC"
                               BorderStyle="None" BorderWidth="1px" CellPadding="3"
                               EnableModelValidation="True"
                               onpageindexchanging="gdvAssetType_PageIndexChanging"
                               onrowcommand="gdvAssetType_RowCommand" Width="747px">
                               <Columns>
                                   <asp:TemplateField HeaderText="Sr No.">
                                       <ItemTemplate >
                                           <asp:Label ID="lbSerialNo" runat ="server" Text='<%#Container.DataItemIndex+1 %>'></asp:Label>
                                       </ItemTemplate>
                                       <ItemStyle HorizontalAlign="Center" VerticalAlign="Middle" />
                                   </asp:TemplateField>
                                   <asp:BoundField HeaderText="Asset Type" DataField="AssetType">
                                   <ItemStyle HorizontalAlign="Center" VerticalAlign="Middle" />
                                   </asp:BoundField>
                                   <asp:TemplateField HeaderText="Edit">
                                       <ItemTemplate >
                                            <asp:ImageButton ID="imgbtnEdit" runat ="server" CommandArgument ='<%#Eval("AssetTypeId") %>' CommandName ="EditAssetType" ImageUrl ="../_img/ico_edit_new.gif"  CausesValidation ="false" ToolTip ="Edit Asset Type"/>
                                       </ItemTemplate>
                                       <ItemStyle HorizontalAlign="Center" VerticalAlign="Middle" />
                                   </asp:TemplateField>
                                   <asp:TemplateField HeaderText="Delete">
                                       <ItemTemplate >
                                           <asp:ImageButton ID="imgbtnDelete" runat ="server" CommandArgument ='<%#Eval("AssetTypeId") %>' CommandName ="DeleteAssetType"  ImageUrl ="../_img/ico_del_new_on.gif" CausesValidation ="false" OnClientClick="if (!confirm('Do you want to delete this user ?')) return false;"  ToolTip ="Delete Asset Type"/>
                                       </ItemTemplate>
                                       <ItemStyle HorizontalAlign="Center" VerticalAlign="Middle" />
                                   </asp:TemplateField>
                               </Columns>
                               <FooterStyle BackColor="White" ForeColor="#000066" />
                               <HeaderStyle BackColor="#006699" Font-Bold="True" ForeColor="White" />
                               <PagerSettings Position="TopAndBottom" />
                               <PagerStyle BackColor="White" ForeColor="#000066" HorizontalAlign="Left" />
                               <RowStyle ForeColor="#000066" />
                               <SelectedRowStyle BackColor="#669999" Font-Bold="True" ForeColor="White" />
                           </asp:GridView>

protected void Page_Load(object sender, EventArgs e)
   {
       try
       {
           if (Session["Username"].ToString() != "" && Session["Username"] != null && Session["Role"].ToString() != "" && Session["Role"] != null && Session.Count != 0)
           {
               if (!IsPostBack)
               {

                   FillGDVAssetTypes();
               }
           }
           else
           {
               Response.Redirect("../Login.aspx");
           }

       }
       catch { Response.Redirect("../ErrorPage/Error.aspx"); }
       finally { }
       //AssignRights();
   }