I have RetrieveDataEventArgs that updates the ultragrid below and overwrites the sum function with last value for column specified.  When I export this to MS Excel it is reverting back to the Windows Application view sum function.  How do I retain changes made in the class event when passing to MS Excel?

public UiEventResult AfterRetrieveData_111(object sender, RetrieveDataEventArgs e)

for (int i = 0; i < rowCount; i++)
{
     foreach (UltraGridChildBand childBand in ultraGrid1.Rows[i].ChildBands)
     {
     foreach (UltraGridRow row in childBand.Rows)
         {
           row.Cells["summaryBandColumn"].Value = row.ChildBands.LastRow.Cells["summaryBandColumn"].Value;
         }
      }

}