return selected row from filtered grid

I'm using ASP.net 2.0 with vb 2005 and sql 2005.  
When I filter the gridview and press select (using the hyperlink on the grid - see below) on a row I'm getting a completely different row.  It's as though the select button is working on the unfiltered gridview.
The gridview is like this.

<asp:Panel ID="Panel1" runat="server" ScrollBars="Both" Height="480px" Width="100%">

        <asp:GridView  ID="Gridview1" runat="server" AllowSorting="True" Font-Names="Arial"
        Font-Size="Small"   RowStyle-Wrap="False" BackColor="White" BorderColor="Silver"  
        DataKeyNames="PrimaryKey"  >
            <RowStyle Wrap="False" />
            <Columns>
                <asp:CommandField ShowSelectButton="True" />
            </Columns>
           
        </asp:GridView>
</asp:Panel>

When the user selects items to filter the filters are passed to a stored proc as a parameter.

create proc [dbo].[SP]
@ExtraFilters nvarchar(MAX)=null
as
Declare @strsql nvarchar(max)

set @strsql='
 select *
          from Xref xref (nolock)
            inner join Future fut (nolock)
            on xref.root = fut.root
            inner join Master m (nolock)
            on fut.RIC = m.RIC
where '+  @ExtraFilters +
' order by xref.root

exec (@strsql)

When I press select alongside a grid row, how can I make it select a row from the filtered gridview as opposed to the unfiltered gridview?