Issue with displaying products from a category

Hello,
I tried to find some solution on this issue but I only found several topics where people have the same problem than me, but without any answer !
The fact is that when you want to display the products from a certain category, you have the Woocommerce shortcode. But the issue is that on some theme (I’m with Gantry currently), what you get is something which is completely different from what you have with the other shortcodes (the background, the borders, the placement of the images, the font of the description … are different).
When analysing with the web explorer, I can see that a “pre” is added (which is not the case for the other shortcodes).
Is there anyone that can explain this and give some potential solutions, as this kind of function is very helpful.
Many thanks in advance.
Pat
http://wordpress.org/extend/plugins/woocommerce/