Problem creating grid in code behind

[Web Services]

I'm having trouble with post backs on a grid where the columns are created in the code behind. Essentially the columns that go in this grid come from a table, but an administrator has another page where they select what columns from the table show in the grid. So, I have table that stores column names and I dynamically add the columns with their header text and data field id based on this table that stores the columns that need to show. I then dynamically create the select statement, set that as the select command to a sqldatasource and bind it. When you load the page initially everything works fine. However, when you click some paging or sorting, it adds a bunch of extra columns. You can see the before and after here
http://imgur.com/a/gO28G#nOVo1 


Here is my ascx

<telerik:radgrid ID="gradeGrid" runat="server" AllowPaging="True" GridLines="None"
            CellPadding="5" AutoGenerateColumns="false" Width="850px" Skin="Metro" >
        </telerik:radgrid>
        <asp:SqlDataSource ID="SqlDataSource1" runat="server" ConnectionString="<%$ ConnectionStrings:connection %>">
        </asp:SqlDataSource>

here is my code behind

Dim conn = System.Configuration.ConfigurationManager.ConnectionStrings("connection").ToString

   'this sub adds a column to the rad grid
   Protected Friend Sub addColumn(ByVal dataField As String, ByVal header As String)

       Dim col As New GridBoundColumn
       col.DataField = dataField
       col.HeaderText = header
       gradeGrid.MasterTableView.Columns.Add(col)

   End Sub 'addColumn

   Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load

       If (Not Page.IsPostBack) Then

           bindGrid()
           gradeGrid.DataBind()

       End If 'if its not a  post back

   End Sub

   'this sub gets the data for the rad grid
   Protected Sub bindGrid()

       Dim reader As SqlDataReader
       'add the columns we know about
       addColumn("lgrade", "Letter Grade")
       addColumn("ngrade", "Percent Grade")
       addColumn("Course Code", "sectno")
       addColumn("Completed", "enddate")

       Dim itemSql = "SELECT lgrade, ngrade, sectno, enddate, "
       'now find all the other ones we need
       Dim sql = "SELECT columnName, label FROM hstuclsDefinedColumns ORDER BY position"
       Using myconn As New SqlConnection(conn)

           myconn.Open()

           reader = New SqlCommand(sql, myconn).ExecuteReader()
           If (reader.HasRows) Then

               While reader.Read()
                   addColumn(reader("columnName"), reader("label"))
                   itemSql &= "[" & reader("columnName") & "]" & ", "
               End While 'reader.read
               reader.Close()
           End If 'if reader.hasrows

           itemSql &= " 'blah' FROM hstucls WHERE stuid = " & MyFunctions.getStudentId

           myconn.Close()
       End Using 'using myconn

       SqlDataSource1.SelectCommand = itemSql

       gradeGrid.DataSource = SqlDataSource1

   End Sub 'bindGrid

   Protected Sub gradeGrid_NeedDataSource(ByVal sender As Object, ByVal e As Telerik.Web.UI.GridNeedDataSourceEventArgs) Handles gradeGrid.NeedDataSource
       bindGrid()
   End Sub

I'm sure it's something stupid, I just don't see what it is. Thanks!

[Web Services]

Found my problem via another forum. Had to change

Dim col As New GridBoundColumn
col.DataField = dataField
col.HeaderText = header
gradeGrid.MasterTableView.Columns.Add(col)

to

Dim col As New GridBoundColumn
gradeGrid.MasterTableView.Columns.Add(col)
col.DataField = dataField
col.HeaderText = header

Move the columns.add method per your example. Why does it cause issues on the post back but not on the page load?