To reproduce:
1 - Add a grid view in a form.
2 - Add 14 - 17 records in grid view.
3 - Allow alternating color for grid view.
4 - Do sorting by clicking on header column (click 3 times).
5 - Alternating color display wrong position.

Workaround:
void radGridView1_SortChanged(object sender, GridViewCollectionChangedEventArgs e)
{
    foreach (GridRowElement row in this.radGridView1.TableElement.ViewElement.ScrollableRows.Children)
    {
        row.Synchronize();
    } 
}