When a RadGridView cell has a validation error, a red border will appear around the cell. In this case, the top validation border is missing on the first row cells. As a workaround, you can move the ContentPresenters of the cells a little bit in the loaded event of the control.

private void RadGridViewView_Loaded(object sender, System.Windows.RoutedEventArgs e)
{
    var treeListView = sender as RadTreeListView;
    var editorPresenters = treeListView.ChildrenOfType<ContentControl>().Where(x => x.Name == "PART_ContentPresenter" && x.ParentOfType<GridViewCell>() != null);
    foreach (var item in editorPresenters)
    {
        item.Margin = new System.Windows.Thickness(1);
    }
}

Per the thread at "http://www.telerik.com/forums/isexpandablebinding-requires-user-interaction-with-control-to-take-effect" I have modified the IsExpandedRowBinding sample to recreate the problem. I modified the button to expand and collapse the first row. To reproduce the problem:

1. Expand the first row.
2. Scroll down so the first row is not visible but it's children are visible.
3. Press the button. The expected behavior is the first row should collapse but nothing happens.
4. Scroll up so the first row is visible. The first row collapses.