title: Kendo UI grid aggregation "sum" not working
body: <p>I exactly followed the examples on Kendo UI's website. All data shows fine, but all the operation of "sum" not happening. So in the groupFooterTemplate, all columns shows the last item in the grid including the "average" column. I have been working on this for a few days and just cannot figure out what went wrong.
      Did this happen to anyone? </p>
  
  <pre><code>$scope.vmResyncGridOptions = {
      dataSource: {
          data: $scope.vmDataSource,
          scheme: {
                model: {
                    id: "vmName",
                    fields: {
                        vmName: { type: "string" },
                        vdiskName: { type: "string" },
                        total: { type: "number" },
                        synced: { type: "number" },
                        percent: { type: "number" }
                    }
               }
          },
          group: {
              field: "vmName",
              aggregates: [
                  { field: "vdiskName", aggregate: "count" },
                  { field: "total", aggregate: "sum" },
                  { field: "synced", aggregate: "sum" },
                  { field: "percent", aggregate: "average" }
              ]
          },
          aggregate: [
              { field: "vdiskName", aggregate: "count" },
              { field: "total", aggregate: "sum" },
              { field: "synced", aggregate: "sum" },
              { field: "percent", aggregate: "average" }
          ]
        },
        sortable: false,
        scrollable: true,
        pageable: true,
        groupable: true,
  
        //height: ($scope.screenHeight-110)*0.70-8,
        columns: [
            {
                field: "vdiskName",
                title: $scope.translation.Resync_Table_VDisk_Name,
                aggregates: ["count"],
                groupFooterTemplate: "Count: #=count#"
            },
            {
                field: "total",
                title: $scope.translation.Resync_Table_Total_Bytes,
                aggregates: ["sum"],
                groupFooterTemplate: "Total: #=sum#"
            },
            {
                field: "synced",
                title: $scope.translation.Resync_Table_Has_Resynced,
                aggregates: ["sum"],
                groupFooterTemplate: "Total Resynced: #=sum#"
            },
            {
                field: "percent",
                title: $scope.translation.Resync_Table_VDisck_Completed,
                aggregates: ["average"],
                groupFooterTemplate: "Percent: #=average#"
            }
          ]
      };
  </code></pre>