Load event fires twice and QueryString becomes empty!!

Hello,

I'm trying to do one page with two listboxes that filers one grid.

The only requirement is that the selection made by the user must be reflected in the URL so that it can be sent by mail to colleagues with the selection already made

The problem is that Load event fires twice.
First time all parameters are transmitted correctly.
The second time the whole QueryString disappears!!

ASPX Directive:

<%@PageLanguage="vb"uiCulture="en-US"culture="de-DE"MasterPageFile="XTAB_WO.master"AutoEventWireup="false"CodeFile="LC1vsLC2.vb"Inherits="LC1vsLC2"ClientIDMode="Predictable"%>

ASPX Code:

<asp:listbox clientidmode="Static" id="LstTipo" style="width:150px;height:100px;" runat="server" datasourceid="SqlDataSource2" datatextfield="FLD_RESULTADO" datavaluefield="FLD_RESULTADO">
<asp:listbox clientidmode="Static" id="LstTMA" style="width:150px;height:100px;" runat="server" datasourceid="SqlDataSource4" datatextfield="FLD_MOD3" datavaluefield="FLD_MOD3">

<dx:ASPxGridView ID="gridview1" runat="server" AutoGenerateColumns="true" DataSourceID="SqlDataSource1"></dx:ASPxGridView><asp:SqlDataSource ID="SqlDataSource1" runat="server" ConnectionString="<%$ ConnectionStrings:MyCCnn %>"></asp:SqlDataSource><asp:Button ID="Button1" runat="server" Text="Select" style="width:150px;" OnClientClick="Populate();"/><asp:SqlDataSource ID="SqlDataSource2" runat="server"
		ConnectionString="<%$ ConnectionStrings:hacheConnectionString %>"
		SelectCommand="select '(ALL)' FLD_RESULTADO UNION ALL select distinct FLD_RESULTADO from XXXXXXXXXXXXX"></asp:SqlDataSource><asp:SqlDataSource ID="SqlDataSource4" runat="server"
		ConnectionString="<%$ ConnectionStrings:hacheConnectionString %>"
		SelectCommand="select '(ALL)' FLD_MOD3 UNION ALL select distinct FLD_MOD3 from XXXXXXXXXXXXX"></asp:SqlDataSource><script type="text/javascript" language="javascript">function removeParam(key, sourceURL) {var rtn = sourceURL.split("?")[0],
			param,
			params_arr = [],
			queryString = (sourceURL.indexOf("?") !== -1) ? sourceURL.split("?")[1] : "";if (queryString !== "") {
                params_arr = queryString.split("&");for (var i = params_arr.length - 1; i >= 0; i -= 1) {
                    param = params_arr[i].split("=")[0];if (param === key) {
                        params_arr.splice(i, 1);
                    }
                }
                rtn = rtn + "?" + params_arr.join("&");
            }return rtn;
        }     function Populate() {var tma = document.getElementById("LstTMA");var tipo = document.getElementById("LstTipo");var fe = "";var miurl="";var miurlIni="";var valor = "";
	    miurlIni = window.top.location.href + "?";if (tipo.selectedIndex >= 0) {var selectedtipo = tipo.options[tipo.selectedIndex].text;
                miurl = removeParam("tipo", miurl);
                valor = (selectedtipo == "(ALL)") ? '0' : selectedtipo;
                miurl = miurl + "&tipo=" + valor.replace(" ","_");
            }if (tma.selectedIndex >= 0) {var selectedtma = tma.options[tma.selectedIndex].text;
                miurl = removeParam("tma", miurl);
                valor = (selectedtma == "(ALL)") ? '0' : selectedtma;
                miurl = miurl + "&tma=" + valor;
            }window.top.location.href = miurlIni + miurl.substring(1,999);
        }</script>   



CODE-BEHIND:


    Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
        Dim q As String, q_count As String, x As Integer, NumR As Long
        Dim dv As Object

        Dim mpContentPlaceHolder As ContentPlaceHolder
        Dim ddlRp As ASPxRoundPanel
        Dim LstTipo As ListBox, StTipo As String
        Dim LstTMA As ListBox, StTma As String


        mpContentPlaceHolder = CType(Master.FindControl("ContentHolder"), ContentPlaceHolder)
        If Not mpContentPlaceHolder Is Nothing Then
            ddlRp = CType(mpContentPlaceHolder.FindControl("ASPxRoundPanel3"), ASPxRoundPanel)
            If Not ddlRp Is Nothing Then
                LstTipo = CType(ddlRp.FindControl("LstTipo"), ListBox)
                LstTMA = CType(ddlRp.FindControl("LstTMA"), ListBox)
            End If
        End If

        If Request.QueryString.Count > 0 AndAlso ((Not Request.QueryString("pais") Is Nothing) Or (Not Request.QueryString("y4m2d2") Is Nothing) Or (Not Request.QueryString("tipo") Is Nothing) Or (Not Request.QueryString("tma") Is Nothing)) Then
            StTipo = "" : StTma = ""': Sty4m2d2 = "" 

            If Not (Request.QueryString("tipo") Is Nothing) AndAlso Request.QueryString("tipo").ToString() <> "" Then
                If Request.QueryString("tipo") = "0" Then
                    LstTipo.SelectedValue = "(ALL)"
                    StTipo = ""
                Else
                    LstTipo.SelectedValue = Replace(Request.QueryString("tipo"), "_", " ")
                    StTipo = " AND FLD_RESULT='"& Replace(Request.QueryString("tipo"), "_", "") & "'"
                End If
            End If

            If Not (Request.QueryString("tma") Is Nothing) AndAlso Request.QueryString("tma").ToString() <> "" Then
                If Request.QueryString("tma") = "0" Then
                    LstTMA.SelectedValue = "(ALL)"
                    StTma = ""
                Else
                    LstTMA.SelectedValue = Replace(Request.QueryString("tma"), "_", " ")
                    StTma = " AND FLD_MOD3='"& Replace(Request.QueryString("tma"), "_", "") & "'"
                End If
            End If

            q = "SELECT " & StFieldsQuery & " FROM V_BUDA_LC1vsLC2 WHERE 1=1 " & StTipo & StTma '& Sty4m2d2 '& " ORDER BY FLD_ID"
            q_count = "SELECT count(*) NumR FROM V_BUDA_LC1vsLC2 where 1=1 " & StTipo & StTma '& Sty4m2d2

            SqlDataSource11.SelectCommand = q_count

            dv = CType(SqlDataSource11.Select(DataSourceSelectArguments.Empty), DataView)
            NumR = CType(dv.Table.Rows(0)(0), Integer)
            If (NumR > 0) Then
                SqlDataSource1.SelectCommand = q

                gridview1.Visible = True
                LblNoData.Visible = False
            Else
                gridview1.Visible = False
                LblNoData.Visible = True
            End If
        Else
            gridview1.Visible = True
            LblNoData.Visible = False

            q = "SELECT * FROM V_BUDA_LC1vsLC2 WHERE 1=0"
            SqlDataSource1.SelectCommand = q
        End If

        Page.DataBind()
    End Sub