Strange border around images with captions

I'm having a weird issue with styling, and I'm at a loss with how to fix it. I've been revamping my personal site lately with Atahualpa (which I've used to build three sites now, awesome theme), and I'm stuck on a problem with captioned images. When I give an image a caption, it adds about 5px on either side of the image with the background color of the caption, as if the div is to wide for the image. I've been over it dozens of times in Firebug, but I can't seem to figure out the culprit. I put up a test post showing my problem here. I changed the background color to red to highlight the problem:

http://www.androsko.com/post/test-post-2

The problem is not present on captionless images like this one:

http://www.androsko.com/post/test-post-1

What I'd like is to get rid of the padding on the left and right of the image so that the caption box is also the same width as the image above it. Everything else is the way I want it except that, and I have no idea where it's coming from. The only thing I found was an element.style that was setting the width to 210px (the image in test post 2 is 200px wide), but I'm not sure how to work around that. Any help would be much appreciated, as I'd love to use captions but I hate that padding.

My specs:
Wordpress 2.9.2
Atahualpa 3.4.6 (I've been having this issue at least since 3.4.4)