I am using XamWebGrid 10.1 with ColumnLayout to show Parent/Details, and using the ContextMenu from the Siliverlight Control toolkit.  It never expands any of the rows. 

        private void dg_MouseRightButtonDown(object sender, MouseButtonEventArgs e)
        {
            e.Handled = true;
        }
 
        private void dg_MouseRightButtonUp(object sender, MouseButtonEventArgs e)
        {
            cMenu = new ContextMenu();
            menuItem = new MenuItem();
            menuItem.Header = "Expand All";
            cMenu.Items.Add(menuItem);
            menuItem.Click += new RoutedEventHandler(menuItem_Click);
 
            menuItem = new MenuItem();
            menuItem = new MenuItem();
            menuItem.Header = "Collapse All";
            cMenu.Items.Add(menuItem);
            menuItem.Click += new RoutedEventHandler(menuItem_Click);
 
            cMenu.IsOpen = true;
            cMenu.HorizontalOffset = e.GetPosition(LayoutRoot).X;
            cMenu.VerticalOffset = e.GetPosition(LayoutRoot).Y;
        }
 
        void menuItem_Click(object sender, RoutedEventArgs e)
        {
            MenuItem mnu = sender as MenuItem;
 
            switch (mnu.Header.ToString())
            {
                case "Expand All":
                    foreach (Row r in dg.Rows)
                    {
                        if (r.RowType == RowType.DataRow)
                            ExpandAllChildRows(r);
                    }
                    break;
                case "Collapse All":
                    foreach (Row r in dg.Rows)
                    {
                        if (r.RowType == RowType.DataRow)
                            CollapseAllChildRows(r);
                    }
                    break;
                default:
                    break;
            }
        }

        private void ExpandAllChildBands(ChildBand parentBand)
        {
            foreach (Row r in parentBand.Rows)
            {
                r.IsExpanded = true;
                if (r.HasChildren)
                    ExpandAllChildRows(r);
            }
        }
 
        private void ExpandAllChildRows(Row parentRow)
        {
            foreach (ChildBand cb in parentRow.ChildBands)
            {
                cb.IsExpanded = true;
                if (cb.HasChildren)
                    ExpandAllChildBands(cb);
            }
        }
 
        private void CollapseAllChildBands(ChildBand parentBand)
        {
            foreach (Row r in parentBand.Rows)
            {
                r.IsExpanded = false;
                if (r.HasChildren)
                    CollapseAllChildRows(r);
            }
        }
 
        private void CollapseAllChildRows(Row parentRow)
        {
            foreach (ChildBand cb in parentRow.ChildBands)
            {
                cb.IsExpanded = false;
                if (cb.HasChildren)
                    CollapseAllChildBands(cb);
            }
        }