So it looks like the thematic_page_title function is adding the wrong permalink for the attachment.php template. Basically, the link in the .page-title of an attachment page points to the current page instead of it’s parent page.
I’m not sure if this is the best way to fix this, but when I go to content-extensions.php and add global $post; to the beginning of the thematic_page_title function, it fixes the permalink.
Example:
function thematic_page_title() {
global $post;
$content = '';
if (is_attachment()) {
$content .= '<h2 class="page-title"><a href="';
$content .= get_permalink($post->post_parent);
$content .= '" rev="attachment"><span class="meta-nav">« </span>';
$content .= get_the_title($post->post_parent);
$content .= '</a></h2>';
…