WCF Data Service Query seems to be retrurning duplcate rows on repeated queries

Question

Hello, I have a data class that return some objects from a wcf dataservice to a silverlight app:

void ExecuteWipReportQuery(DataServiceQuery qry) { context = new StaffKpiServices.HwfStaffKpiEntities(theServiceRoot); qry.BeginExecute(new AsyncCallback(a => { try { IEnumerable results = qry.EndExecute(a); OnDataLoadingComplete(new WipReportByMonthEventArgs(results)); } catch (Exception ex) { OnDataLoadingError(ex); } }), null); }

The view model then get these results and adds them to an observable collection:

void wipReportDataContainer_DataLoadingComplete(object sender, Domain.WipReportByMonthEventArgs e) { Application.Current.RootVisual.Dispatcher.BeginInvoke(() => { this.wipReport.Clear(); string s = "";

          foreach (StaffKpiServices.WipReportByMonth r in e.Results)
          {
              //this.wipReport.Add(r);
              //s += r.ClientCode;
              this.wipReport.Add(new StaffKpiServices.WipReportByMonth
              {
                  ClientCode = r.ClientCode,
                  ClientGroup = r.ClientGroup,
                  ClientName = r.ClientName,
                  ClientType = r.ClientType,
                  FinancialYear = r.FinancialYear,
                  Month = r.Month,
                  OSDebt = r.OSDebt,
                  OSDisb = r.OSDisb,
                  OSOther = r.OSOther,
                  OSTime = r.OSTime,
                  OSTotal = r.OSTotal,
                  PartnerUserName = r.PartnerUserName,
                  PracName = r.PracName,
                  Recov = r.Recov,
                  RecovFees = r.RecovFees,
                  RecPerc = r.RecPerc,
                  SicCode = r.SicCode,
                  SicParentName = r.SicParentName,
                  StaffName = r.StaffName,
                  YTDFees = r.YTDFees,
                  YTDTime = r.YTDTime
              });

              s += r.ClientCode + " ";

          }
          string s2 = "";
          foreach (var p in this.wipReport)
          {
              s2 += p.ClientCode + " ";
          }
          OnPropertyChanged("WipReport");
          if (null != LoadComplete)
          {
              LoadComplete(this, EventArgs.Empty);

          }
      });
    }

Everything works ok, but if the data is refreshed two or three times, then the collections retrun contains the right number of objects, but all with duplicate properties. There seems to be no reason why, it is as if the foreach is not working on the collection, but at the same time not returning any errors. Any ideas?