Papervision glitch

Hi there
I’m fooling around with papervision and i’m getting this strange glitch kind of rendering.
Basically i’m just creating alot of bars with a FlatShadeMaterial. All of them have the same light. Then i’m positioning them one next to another to form a bigger bar. Finally, each bar is displaced randomly in z position.

i’ve attached a screenshot showing the glitch.
does anybody have any idea what could cause this kind of behaviour?