Unable to link products to external sites

Hi. I've just updated MarketPress and I'm now having problems linking new products to external sites. I have set my new lines up in exactly the same way as my old ones, but in the older products, the product title and image link to the external site as expected. The later additions link to the single product page on my site. The template hasn't changed and I can' work out what the problem is - help!!
As an example, on the Button Down Dresses page, the top item (Jawbreaker Sexy Emo Punk Skull Roses Lace Skater Flare Shirt Party Dress (Amazon)) is new and links incorrectly. All the others are older products and seem to work fine.