Any way to stop Gallery Shortcode from including the Featured Image?

My blog is based on the AutoFocus+ theme, which uses the Featured Image option to attach the main image to each post. Which all works very well.
The trouble I’m having is when I want to add an image gallery to a post (using the Gallery shortcode), the Featured Image gets automatically inserted into the gallery, and I don’t want it to be.

see: http://www.jjpare.com/blog/?p=123
note the double first image

The images in the gallery are uploaded at larger sizes than the Featured image is (1200-1500px vs. 800px), so I’d rather not have to use the Featured image in place of the full-size one if I can help it.

I’m just wondering if there’s a reason the Gallery keeps picking up the Featured image, and if there’s a way to stop it from happening.

Thanks.