I just noticed this too. Looks like the issue is related to the plugin trying to hook directly to the default WP nonce, and the name of the default nonce action was updated in WP3.5
A quick patch is here: in abt-relative-urls.php:
--- abt-relative-urls.php 2012-12-18 12:45:32.641102283 -0800
+++ abt-relative-urls.php 2012-12-18 12:44:43.237104028 -0800
@@ -167,7 +167,7 @@
/* */
$posted_type = $_POST['post_type'];
$posted_id = $_POST['post_ID'];
- $nonce_name = 'update-' . /*$post->post_type*/ $posted_type . '_' . /*$post_ID*/ $posted_id;
+ $nonce_name = 'update-post_' . /*$post_ID*/ $posted_id;
if ( empty($_POST) || ! check_admin_referer($nonce_name) ){
return $post_ID;
}
Basically, WP used to use a nonce action on updating posts named update_{$post_type}_{$post->ID}
, and the plugin is looking for that. The action name is just update-post_{$post->ID}
, and that makes the plugin choke.