To Reproduce:
Add a RadCarousel - add less than 5 items - you can see that the behavior is incorrect

Workaround:
this.carousel.Items.Add(new RadButtonElement("Text"));
for (int i = 0; i < 4; i++)
{
    this.carousel.Items.Add(new RadButtonElement(){ Visibility = ElementVisibility.Hidden });
}

http://www.telerik.com/forums/using-a-radcarousel-with-a-variable-number-of-items-less-than-5