ItemCommand of DataList in UpdatePanel is not fired on Postback

I have a popup panel which contains an UpdatePanel, which contains a DataList. Table rows are populated using ItemTemplate and there is a LinkButton generated on each row for deleting this row. I would like to delete this record in the DataList's ItemCommand event handler and rebind the DataList.

However, after I click a "delete" button in the DataList, ItemCommand is not fired. I've already checked if IsPostBack in my Page_Load and only do Datalist.Databind() if it's not a postback. Normally I would expect first Page_Load and then list_ItemCommand being called after I click a delete button in the DataList, but list_ItemCommand is not called as expected. And nothing is then displayed in DataList which is inside the UpdatePanel.

And stranger, if I remove the IsPostBack check in Page_Load, that being said, rebind the DataList in every Page_Load, ItemCommand will be caught and list_ItemCommand is called. This is against the answers in many other posts "ItemCommand event will be canceled if DataList is rebinded during PostBack".

Code behind:

Protected records As New List(Of Record)

Protected Sub Page_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
    Set some page properties...
    If Not Page.IsPostBack Then
        GetListOfRecordFromDatabase()
        datalist.DataSource = records
        datalist.DataBind()
    End If
End Sub

Protected Sub datalist_ItemCommand(ByVal source As Object, ByVal e As System.Web.UI.WebControls.DataListCommandEventArgs) Handles datalist.ItemCommand
    Select Case e.CommandName.ToLower
        Case "delete"
            For Each c As Record In records
                If c.Id = e.CommandArgument Then
                    records.Remove(c)
                    Exit For
                End If
            Next
            DeleteRecordFromDatabase(e.CommandArgument)
    datalist.DataSource = records
    datalist.DataBind()
    End Select
End Sub

Controls:

<asp:Content ID="content1" runat="server" ContentPlaceHolderID="Content1PlaceHolder">
    <asp:LinkButton ID="btnpopup" runat="server" OnClientClick="javascript:return popup()"></asp:LinkButton>
        <asp:ScriptManagerProxy ID="ScriptManagerProxy1" runat="server" EnableViewState="false" >
        </asp:ScriptManagerProxy>

        <asp:Panel ID="PanelPopup" runat="server" style="display:none;">

            <asp:UpdatePanel ID="UPPopup"  runat="server"  UpdateMode="conditional" EnableViewState="false">
                <ContentTemplate>
                <div id="divPopup1" runat="server">

                    <table id="table1" cellpadding="2" cellspacing="1" width="500" border="0" >
                        <asp:DataList ID="datalist" runat="server" OnItemCommand="datalist_ItemCommand">
                        <ItemTemplate>
                            <tr align="center">
                            <td><%#Container.ItemIndex +1 %></td>
                            <td><asp:Label ID="Label1" runat="server" Text='<%# eval("Name") %>'></asp:Label></td> 
                            <td><asp:Label ID="Label2" runat="server" Text='<%# eval("Color") %>'></asp:Label></td> 
                            <td><asp:LinkButton ID="Delete" CommandName="Delete" runat="server" Text="Delete" CommandArgument='<%# eval("Id") %>' ></asp:LinkButton></td>
                            </tr>
                        </ItemTemplate>
                        </asp:DataList>
                    </table> 
                </div>
                </ContentTemplate>
            </asp:UpdatePanel>
            <div style="text-align:center;"><br />
                <asp:Button ID="BtnSavePopup" runat="server" Text="Save and Close"/> 
            </div>                   
        </asp:Panel>

    <script type="text/javascript">
        function popup() {
            return mypagehelper.openAsModalPopup("<% =PanelPopup.ClientID%>");
        }
    </script>
</asp:Content>

Further more, I tried to grab the ControlID and the Control who raised the event during Postback using this code:

If IsPostBack Then
  Dim CtrlID As String = String.Empty
  If Request.Form("__EVENTTARGET") IsNot Nothing And
     Request.Form("__EVENTTARGET") <> String.Empty Then
     CtrlID = Request.Form("__EVENTTARGET")
     Dim postbackControl As System.Web.UI.Control = Page.FindControl(CtrlID)
  Else      
End If

And I found that I can get my CtrlID as "ctl00$datalist$ctl08$Delete" but the postbackControl is Nothing. While on my other normal pages I can get both the controlID and actual control(which is a LinkButton) who raised the event.