Composer render style - silhouette and technical - strange hidden line behaviour

Hi,

I'm seeing some strange line display behavior  - I've turned certain components to Silhouette render style, and i'm keeping certain components in Technical style.

All components are displaying random hidden lines which makes the picture un-usable.

See snippet of screenshot below:

is this normal behaviour? Does anyone recognise this and does it point to certain settings?

It could just be a symptom of insufficient PC hardware because sometimes I get the image i expect.. but i am very new to Solidworks and Composer so i'm probably (hopefully) missing something simple!

Thanks for the help!

Jon

SolidworksComposer