Wijmo 5 flex chart doesn't work with knockout foreach binding

Question

I want dynamically update the values(or add extra legend item) on my chart thus I can't use the 'hardcoded' html markup from the flexchart example page. the problem is that foreach binding inside wjFlexChart block doesn't work at all. here's my code:

View:

<div data-bind="wjFlexChart: { itemsSource: data, bindingX: 'week' }">
      <div data-bind="foreach: $data.legend">
            <div data-bind="wjFlexChartSeries: { name: name, binding: value}"></div>
      </div>
</div>

---

ViewModel:

data = new wijmo.collections.ObservableArray();
weeks = 'wk1,wk2,wk3,wk4,wk5,wk6,wk7,wk8'.split(',');
...
for (var i = 0; i < this.weeks.length; i++) {
   this.data.push({
     week: this.weeks[i],
     legend: [{
        name: 'name1_'+i, 
        value: Math.random() * 10
     },{
        name: 'name2_'+i, 
        value: Math.random() * 10
     }]
   });
}

Any ideas?