Marketpress – category view pulling different products in

In category view, instead of just showing all the products in a category I have chosen, Marketpress seems to pull in an image from elsewhere and make the category link, link to that images product, if that makes sense.

For example, see here http://www.30daychallenges.nikkipilkington.com/30day/store/products/category/twitter/

Now, much as I like seeing my mug bandied around, it shouldn’t be at the top of there as it’s the thumbnail for an ebook I don’t have a cover from.

That page should list all the Twitter downloads (ones I’ve tagged with Twitter, including the one with the pic as the thumbnail).

If you look, ‘product category –> Twitter’ at the top doesn’t link to the category, it links to the ebook that thumbnail comes from.

What am I doing wrong?

If it helps, I’m using Genesis latest version with Serenity child theme.