Wijmo 5 - FlexGrid with Infinite Scrolling

HTML

<link rel="stylesheet" href="http://maxcdn.bootstrapcdn.com/bootstrap/3.2.0/css/bootstrap.min.css">
<link rel="stylesheet" href="http://cdn.wijmo.com/5.latest/styles/wijmo.min.css">
<script src="http://cdn.wijmo.com/5.latest/controls/wijmo.min.js"></script>
<script src="http://cdn.wijmo.com/5.latest/controls/wijmo.grid.min.js"></script>
<script src="http://cdn.wijmo.com/5.latest/controls/wijmo.input.min.js"></script>
<b>Latest Version (5.20193.637) gives error.</b>
<p>ERROR : Uncaught ** Assertion failed in Wijmo: Found duplicate key: 1 Error</p>
<br>
<br>

<div id="flex"></div>

CSS

.wj-flexgrid {
  height: 300px; 
  margin-top:10px;
}

JavaScript

var wijmoGridObject = null;
onload = function() {

        wijmo.grid.FlexGrid.disposeAll('#flex');
        function getWijmoGridDataSource() {
                var data =[];
                data.push({
                    StockItemId: '1',
                    Description: 'StockItem1',
                    Warehouse: '2',
                    WarehouseName: '',
                    Quantity: 2,
                    Price: 1000,
                    Total: 2000
                });
                data.push({
                    StockItemId: '2',
                    Description: 'StockItem2',
                    Warehouse: '4',
                    WarehouseName: '',
                    Quantity: 1,
                    Price: 1000,
                    Total: 1000
                });
                return data;
            }
        wijmoGridObject = new wijmo.grid.FlexGrid(('#flex'),
                {
                    itemsSource: getWijmoGridDataSource(),
                    selectionMode: wijmo.grid.SelectionMode.ListBox,
                    isReadOnly: false,
                    autoSizeMode: wijmo.grid.AutoSizeMode.Both,
                    allowSorting: 0,
                    allowAddNew: false,
                    beginningEdit: function(s, e)
                                {
                                     if (e.col == 2) {
                                        var warehouseColObj = wijmoGridObject.columns[2];
                                        var map = warehouseColObj.dataMap;
                                        if (map) {
                                            var stockId = wijmoGridObject.rows[e.row].dataItem.StockItemId;
                                            map.collectionView.filter = (item) => {
                                                return item.StockItemId == stockId;
                                            }
                                        }
                                    }
                        ...