When I click on a post's Facebook like button on an archive page, the archive url is sent to Facebook instead of the post url (e.g. http://example.com/2013 instead of http://example.com/2013/post-permalink).
The reason for this seems to be a typo in the function facebook_button().
Line 108 of buttons.php is
href="' . $attr['url'] . '"
when it should be
href="' . $atts['url'] . '"