Workaround:
public Form1()
{
    InitializeComponent();

    this.radCarousel1.CarouselElement.AnimationFinished += CarouselElement_AnimationFinished;
}

void CarouselElement_AnimationFinished(object sender, EventArgs e)
{
    if (this.radCarousel1.Items.Count == 6)
    {
        radCarousel1.CarouselElement.AnimationFinished -= CarouselElement_AnimationFinished;
        this.radCarousel1.SelectedIndex--;
    }
}