Kendo: inner grid based on passed datafrom main grid does not update model after change

Question

I have following init function for inner grid.

Date are fetched but after the change od some data in inner grid is not diplayed small red arrow signalizing change on the dataSource (model).

So if i processed update request no changes made in the inner grid is send back in the request (always it send old data).

How can i solve it please and what i'm doing wrong?

I tried to find some solution here and in documentation but without luck.

Thanks for any help.

function detailInit(e) {
      //var dataSource = options.model.get("costCategory");
      console.log(e);
      $("<div/>").appendTo(e.detailCell).kendoGrid({
        dataSource: {
          data: e.data.milestones,
          schema: {
            model: {
              fields: {
                id: {
                  type: "string"
                },
                estimate: {
                  type: "number",
                  nullable: true,
                  defaultValue: null,
                  editable: true
                },
                actual: { type: "number" }
              }
            },
            data: function(response) {
              console.log(response);
              return response;
            },
          },
          pageSize: 10
        },
        scrollable: false,
        sortable: true,
        editable: "incell",
        columns: [
          { field: "id", width: "70px" },
          { field: "milestoneTemplate.name", title:$translate.instant('MILESTONE_TEMPLATE_NAME'), width: "110px" },
          { field: "estimate", title:$translate.instant('ESTIMATE'), width: "110px" },
          { field: "actual", title:$translate.instant('ACTUAL') },
        ]
      });
    };