Dynamisk checkboxlist problem

Jeg har et problem med min dynamiske checklistbox.

Checklistboxen genereres ud fra et DB-opslag og der fungerer sådan set også fint nok. Men når siden reloades (postbackes) forsvinder en af mine listoptions...

Lidt kode:

Sub CheckSMSData(ByVal strSearch As String)
        Dim tTable As DataTable
        Dim rRow As DataRow
        Dim cColumn As DataColumn
        Dim strSearch1 As String

        For Each tTable In objDBDataSet.Tables
            For Each rRow In tTable.Rows
                For Each cColumn In tTable.Columns
                    strSearch1 = (rRow(cColumn.ColumnName))
                    If strSearch1 <> strSearch Then
                        ValCheckDataCompare = 1
                    End If
                Next cColumn               
            Next rRow
        Next tTable

        If ValCheckDataCompare = 0 Then
            show(strSearch)
        End If

        ValCheckDataCompare = 0
        strSearch = ""
        objDBDataSet.Clear()

    End Sub



Sub show(ByVal strSearch As String)
        oCheckBoxList.RepeatDirection = RepeatDirection.Vertical

        If Not (IsPostBack) Then
            oCheckBoxList.Items.Add(New ListItem(strSearch))
        End If

        CheckBoxPlaceholder.Controls.Add(oCheckBoxList)

    End Sub


HTML:
<form id="Form1" method="post" runat="server">
<asp:placeholder id="CheckBoxPlaceholder" runat="server"></asp:placeholder>
</form>