Dissapearing data in a GridView

Question

I have a page with a GridView bound to a custom ObjectDataSource. Grid has a selection ability which triggers FormView to retrieve selected index and use it as a parameter for a SELECT to get details about specific item. The problem is when I select a row in that grid on a page where there are less items than PageSize (Paging is enabled, DataSource is a List) the last item just dissapears and selection is made properly. When I select an item from grid page that has as many items as PageSize nothing dissapears at all. Any help?

My code is nothing out of ordinary. Here's the ObjectDataSource and a GridView (layout ommited):

 <asp:ObjectDataSource ID="gridSource" runat="server" EnablePaging="true" TypeName="film.DBComm"
        SelectMethod="GetPage" SelectCountMethod="GetCount" />
    <asp:ObjectDataSource ID="detailSource" runat="server" TypeName="film.DBComm"
        SelectMethod="GetDetails">
        <SelectParameters>
            <asp:ControlParameter ControlID="ResultGrid" Name="ID" PropertyName="SelectedDataKey.Values[&quot;ID&quot;]" />
        </SelectParameters>
    </asp:ObjectDataSource>
        <asp:GridView ID="ResultGrid" runat="server" DataSourceID="gridSource" DataKeyNames="ID"
            AllowPaging="True" PageSize="20" AutoGenerateColumns="False" BorderStyle="None"
            GridLines="None" EnableSortingAndPagingCallbacks="false" Font-Size="Small" Width="90%"
            CssClass="gridMargins">

            <PagerSettings Mode="NextPreviousFirstLast" FirstPageText="<< Pierwsza" LastPageText="Ostatnia >>"
                NextPageText="Następna" PreviousPageText="Poprzednia" Position="Top" />
            <PagerStyle HorizontalAlign="Center" VerticalAlign="Middle" ForeColor="Orange" BackColor="#F0FFF0"
                Font-Size="Small" />

            <Columns>
                <asp:BoundField DataField="ID" HeaderText="Number" SortExpression="ID" Visible="false" />
                <asp:BoundField DataField="TitleColumn" HeaderText="Title" SortExpression="TitleColumn"
                    ItemStyle-Width="40%" HeaderStyle-Width="40%">
                    <HeaderStyle Width="40%"></HeaderStyle>
                    <ItemStyle Width="40%"></ItemStyle>
                </asp:BoundField>
                <asp:BoundField DataField="OriginalTitleColumn" HeaderText="Original title" SortExpression="OriginalTitleColumn"
                    ItemStyle-Width="35%" HeaderStyle-Width="35%">
                    <HeaderStyle Width="35%"></HeaderStyle>
                    <ItemStyle Width="35%"></ItemStyle>
                </asp:BoundField>
                <asp:CommandField ButtonType="Image" CancelText="Cancel" SelectImageUrl="~/Images/order.gif"
                    SelectText="Order" ShowSelectButton="True" ItemStyle-Width="5%" HeaderStyle-Width="5%">
                    <HeaderStyle Width="5%"></HeaderStyle>
                    <ItemStyle Width="5%"></ItemStyle>
                </asp:CommandField>
            </Columns>
        </asp:GridView>

        <asp:FormView ID="Details" runat="server" DataSourceID="detailSource">
            <ItemTemplate>
                <b>
                    <label>
                        Number
                    </label>
                    <%# Eval("ID") %>
                    ...other fields...
                <asp:LinkButton ID="Order" runat="server" CommandName="Order" CommandArgument="<%# Eval(&quot;ID&quot;) %>"
                    Text="Order" />
            </ItemTemplate>
        </asp:FormView>

And the method that calls a stored procedure from a database and gets a results page:

 public DataTable GetPage(int startRowIndex, int maximumRows)
        {
            SqlConnection conn = new SqlConnection(connectionString);
            SqlCommand cmd = new SqlCommand("GetViewPage", conn);
            cmd.CommandType = CommandType.StoredProcedure;
            cmd.Parameters.AddWithValue("@Start", startRowIndex);
            cmd.Parameters.AddWithValue("@Count", maximumRows);


            SqlDataAdapter adapter = new SqlDataAdapter(cmd);
            DataSet ds = new DataSet();

            try
            {
                adapter.Fill(ds);
                return ds.Tables[0];

            }
            catch (SqlException)
            {
                throw new ApplicationException("Data read error. Try again later.");
            }
        }