Marketpress images / thumbnails need clarification

Hi,

I'm setting up products in Marketpress but can't figure out how the images and thumbs work.

I've set the 'store settings' to: "WP-Thumnail Size" and I've use the 'Set featured image' function in 'edit products', but I'm not getting a thumbnail nor a lightbox pop up.

I'm only getting the full image showing in the product's post.

I'd appreciate some guidance.

Many thanks

Ralf