I need to be load a pivot grid without blocking my UI.  I am using:

ExposureGrid.DataSource.DeferredLayoutUpdate = true;
ExposureGrid.DataSource.LoadSchemaCompleted += (s, e) =>
                {
                    ViewModel.LoadingData = false;
                };
            ExposureGrid.DataSource.LoadSchemaAsync();
            ExposureGrid.DataSource.DeferredLayoutUpdate = false;  

Of course, LoadSchemaCompleted never fires.