seriesMapping seriesMapping = new SeriesMapping();
             foreach (IGroupDescriptor descriptor in chartGrid.GroupDescriptors)
            {
                seriesMapping.GroupingSettings.GroupDescriptors.Add(new ChartGroupDescriptor(getDataMemberName(descriptor)));
            }
            seriesMapping.ItemMappings.Add(new ItemMapping(lastGrouping , DataPointMember.XCategory));
            seriesMapping.ItemMappings.Add(new ItemMapping(lastGrouping , DataPointMember.LegendLabel));
            ChartAggregateFunction aggFunc = getChartAggregation(lbxFunction);
            mapping = new ItemMapping(lbxSumm.SelectedValue.ToString(), DataPointMember.YValue, aggFunc);
            DataColumn col = dt.Columns[lbxSumm.SelectedValue.ToString()];
            if (col != null) mapping.FieldType = col.DataType;
            seriesMapping.ItemMappings.Add(mapping);
            radChart1.DefaultSeriesDefinition = (ISeriesDefinition)getChartType();
            radChart1.ItemsSource = null;
            radChart1.SeriesMappings.Clear();
            radChart1.DefaultView.ChartLegend.UseAutoGeneratedItems = true;
            radChart1.DefaultSeriesDefinition.LegendDisplayMode = LegendDisplayMode.SeriesLabel; 
            DataTable dtSource = dt;
            radChart1.SeriesMappings.Add(seriesMapping);
            radChart1.ItemsSource = dtSource;

1. I have a radgridview with the following sorted items in it; the column has a SortDescriptor with SortDirection="Ascending".
   00 item
   03 item
   05 item
   99 item
2. Rename the cell in the 2nd row in a way that would make it move down 1 position in the list (prepend "06"):
   00 item
   06 03 item
   05 item
   99 item
   The column header shows an up-triangle, indicating ascending sort, but the column is not sorted. 
3. Now rename the first row (prepend "07"):
   06 03 item
   05 item
   07 00 item 
   99 item
   The renamed item "07 00 item" sorted itself properly, but the one that failed in step 2, "06 03 item", is still in the wrong place.