BaseGridBehavior behavior = (BaseGridBehavior)this.radGridView2.GridBehavior;
behavior.UnregisterBehavior(typeof(GridViewDataRowInfo));
behavior.RegisterBehavior(typeof(GridViewDataRowInfo), new MyGridRowBehavior());

public class MyGridRowBehavior : GridDataRowBehavior
{
    public override bool OnMouseDown(MouseEventArgs e)
    {
        typeof(GridRowBehavior).GetField("orderedRows", System.Reflection.BindingFlags.NonPublic |
                                                        System.Reflection.BindingFlags.Instance).SetValue(this, new List<GridViewRowInfo>());
        bool result = base.OnMouseDown(e);

        return result;
    }
}