The Assign method of a column collection doesn't set the ButtonType property of columns

Hi,

I've got a problem showing the correct ButtonType of Treelist command column at runtime, the command column ButtonType was set to ButtonType.Image but it always shows as link instead of Image.

     I noticed that using Treelist.Columns.Assign() function to assign the Treelistcolumn collection doesn't render the correct button type, but when I use Treelist.Columns.Add() to add a command column, the image button shows up correctly. Please see my sample code snippet below, Thanks.

        protected void Page_Load(object sender, EventArgs e)
        {
            if (!Page.IsPostBack && !Page.IsCallback)
            {
                this.AssignColumns();
            }

            this.BindData();
        }
          
          private void BindData()
          {
               trListMain.DataSource = myDatasource;
               trListMain.KeyFieldName = "GUID";
            trListMain.ParentFieldName = "ParentGUID";
      trListMain.DataBind();
            trListMain.ExpandAll();
          }
          
          private void AssignColumns()
          {
               TreeListColumnCollection columnCollection = new TreeListColumnCollection(trListMain);
               TreeListTextColumn code = new TreeListTextColumn();
               TreeListTextColumn description = new TreeListTextColumn();
               TreeListCommandColumn action = new TreeListCommandColumn();
               
               
               code.Caption = "Code";
            code.Name = "Code;
            code.FieldName = "Code";
            code.Width = Unit.Pixel(130);
            columnCollection.Add(code);
            

            description.Caption = "Description";
            description.Name = "Description";
            description.FieldName = "Description";
            columnCollection.Add(description);
               
               action.ButtonType = ButtonType.Image; << This doesn't work.
               action.Width = Unit.Pixel(156);
               action.Caption = "Action";

               action.NewButton.Visible = true;
               action.NewButton.Image.Url = "~/Images/Grid/ButtonNew.png";
               action.NewButton.Image.Width = Unit.Pixel(78);

               action.DeleteButton.Visible = true;
               action.DeleteButton.Image.Url = "~/Images/Grid/ButtonDelete.png";
               action.DeleteButton.Image.Width = Unit.Pixel(78);

               action.UpdateButton.Visible = true;
               action.UpdateButton.Image.Url = "~/Images/Grid/ButtonUpdate.png";
               action.UpdateButton.Image.Width = Unit.Pixel(78);

               action.CancelButton.Visible = true;
               action.CancelButton.Image.Url = "~/Images/Grid/ButtonCancel.png";
               action.CancelButton.Image.Width = Unit.Pixel(78);

               action.EditButton.Visible = true;
               action.EditButton.Image.Url = "~/Images/Grid/ButtonEdit.png";
               action.EditButton.Image.Width = Unit.Pixel(78);
               columnCollection.Add(action);
               
               trListMain.Columns.Assign(columnCollection);
          }