ModalPopupExtender loses dynamically-added table rows on button click - asp.net

Question

VS 2013, ASP.NET 3.5 VB.NET
Page has multiple ModalPopupExtender controls for different popups. One of these popups fills a table with CheckBoxControls and descriptions for up-selling items.
Page Code:
<%# Register Assembly="AjaxControlToolkit" Namespace="AjaxControlToolkit" TagPrefix="ajax" %>
[snip]
<ajax:ModalPopupExtender
runat="server"
ID="mpeUpsell"
popupControlID="pUpsell"
CancelControlID="bGoBack"
BackgroundCssClass="custBackground"
PopupDragHandleControlID="phDragUpsell"
TargetControlID="bHidden"
Enabled="True" />
<asp:Panel runat="server" ID="pUpsell" style="display:none;">
<div runat="server" class="custPopup">
<div runat="server" id="phDragUpsell">
<h3 style="text-align:center;">
<asp:Label
ID="lUpsellHdr"
runat="server"
Text="Check Out these Add-Ons" />
</h3>
</div>
<asp:Label
ID="lAddOnsText"
runat="server" />
[snip]
<asp:Table
ID="tItems"
runat="server"
style="border: 1px solid black;">
[snip] <asp:Button ID="bNext" runat="server" Text="Next --->" />
</td>
</tr>
</table>
<br />
<br />
</div>
</asp:Panel>
The table tItems is populated like so:
For Each dr As DataRow In ds.Tables(0).Rows
tr = New TableRow()
tc = New TableCell()
Dim sName As String = "cbItem_" & CInt(dr("ITEM_ID"))
Dim cb As New CheckBox()
cb.ID = sName
cb.Text = dr("ITEM_DESC").ToString.Trim
If CInt(dr("UGICheckOFF")) = 1 Then
cb.Checked = True
Else
cb.Checked = False
End If
[snip formatting]
tc.Controls.Add(cb)
tr.Cells.Add(tc)
tc2 = New TableCell()
Dim sPrice As String = String.Format("{0:C}", dr("ITEM_PRICE"))
tc2.Text = sPrice
[snip formatting]
tr.Cells.Add(tc2)
tItems.Rows.Add(tr)
Next
The table populates perfectly and shows when I use code-behind to show the mpeUpsell ModalPopupExtender.
The bNext button's handler looks like this:
Protected Sub bNext_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles bNext.Click
If iItemArray IsNot Nothing Then iItemArray = Nothing ' get rid of it
' Handle the Next Button
Dim iCartID As Integer = -1
iCartID = CInt(Session("CartID"))
' iterate the items and add each to cart if not already in cart
iItemArray = New ArrayList()
For Each tr As TableRow In tItems.Rows
For Each tc As TableCell In tr.Cells
For Each ctl As Control In tc.Controls
If TypeOf (ctl) Is CheckBox Then
Dim cb As CheckBox = CType(ctl, CheckBox)
If cb.Checked Then
'if there are checks create array of item IDs checked.
Dim itemid As Integer = CInt(cb.ID.Replace("cbItem_", ""))
iItemArray.Add(itemid)
End If
End If
Next
Next
Next
[snip]
End Sub
When the handler is executed, tItems.Rows.Count is ZERO and the ForEach simply falls through because the table rows are gone.
It is obvious that I have missed something; I just cannot figure out what I have missed.
Thanks,
John.

Answer 1

The solution was to abandon the asp table because it is not stateful in this instance. Instead, I used a gridview and bound a datatable to it, and am able to retrieve the values.
Thanks.