How to set SelectedItem for a ColumnSeries chart from the ViewModel - silverlight-4.0

Question

I have a ColumnSeries chart where I want to control the selected item from the view model. I do this by binding the the SelectedItem of the chart to an object on the view model.
<chartingToolkit:Chart Grid.Row="2" VerticalAlignment="Stretch" HorizontalAlignment="Stretch" BorderThickness="0" MinHeight="200" Margin="0" x:Name="ratingsChart" Style="{StaticResource ChartWithoutLegendStyle}">
<chartingToolkit:Chart.Series>
<chartingToolkit:ColumnSeries x:Name="chartRatingColSeries" IsSelectionEnabled="True"
SelectedItem="{Binding SelectedRatingDistribution, Mode=TwoWay}"
ItemsSource="{Binding RatingsList}"
IndependentValueBinding="{Binding RatingName}"
DependentValueBinding="{Binding NumberOfGoodies}">
</chartingToolkit:ColumnSeries>
</chartingToolkit:Chart.Series>
</chartingToolkit:Chart>
There are various elements on the page which will force the chart's data to be reloaded (via a web service). When I need to reload the charts data (from the view model), I want to set the SelectedItem of the chart to the very first data point. This appears to work EXCEPT the chart does not visually show (in red, by default) the selected item. Here is sample code that reloads data after web service call and resets selected item:
private RatingDistribution _selectedRatingDistribution = new RatingDistribution();
public RatingDistribution SelectedRatingDistribution
{
get { return _selectedRatingDistribution; }
set
{
_selectedRatingDistribution = value;
RaisePropertyChanged("SelectedRatingDistribution");
}
}
private ObservableCollection<RatingDistribution> _lstRatings = new ObservableCollection<RatingDistribution>();
public ObservableCollection<RatingDistribution> RatingsList
{
get { return _lstRatings; }
set
{
_lstRatings = value;
RaisePropertyChanged("RatingsList");
}
}
private void GetRatingsDistributionCompleted(object sender, GetRatingsDistributionCompletedEventArgs e)
{
IsBusy = false;
RatingsList.Clear();
foreach (RatingDistribution rd in e.Result)
RatingsList.Add(rd);
SelectedRatingDistribution = RatingsList[0];
}
Setting the SelectedRatingDistribution from the View model will not visually show the selected item on the chart in red. Any ideas??
Update:
So if I click on a column, the chart correctly shows the selected item in red as so:
But If I set the SelectedItem from view model, the column will not be displayed in red (as the selected item)

Answer 1

Changed function below fixes problem..
private void GetRatingsDistributionCompleted(object sender, GetRatingsDistributionCompletedEventArgs e) {
RatingsList.Clear();
foreach (RatingDistribution rd in e.Result)
RatingsList.Add(rd);
App.Current.RootVisual.Dispatcher.BeginInvoke(new Action(delegate() { SelectedRatingDistribution = RatingsList[0]; }));
}