What am I doing wrong

kendo-tree-list.js

var FolderTree = {

  init: function (target_div) {
    var me = this;

    me.data_source = new kendo.data.TreeListDataSource(
      {
        transport: {
          read: {
            url: "/folder/elements",
            dataType: "jsonp"
          }
        },
        schema: {
          model: {
            id: 'id',
            parentId: 'parentId',
            fields: {
              id: {type: 'number', nullable: false},
              parentId: {type: 'number', nullable: true}
            }
          }
        }
      }
    );

    me.folder_tree = $(target_div).kendoTreeList(
      {
        dataSource: me.data_source,
        height: '100',
        columns: [
          {field: "name", expandable: true, title: "Name"},
          {field: "state_name", title: "State Name"},
          {field: "id"},
          {field: "parentId", title: "Parent"}
        ],
        dataBound: function () {
          $(target_div + ' > .k-grid-content').css('height', '100%');
        }
      }
    ).data('kendoTreeList');
  }

};

/*
Server returns correct jsonp data (using params[:callback]) but also I've tried returning plain json.

I can confirm the data is all loaded with this:
$('#folder_tree_div').data('kendoTreeList').dataSource.data();

No rows appear. It just completes as expected then shows an empty grid with "No records to display".

It displays correctly if I just write some data directly into the dataSource.
*/