AddThis Inserts duplicate meta items

Currently the addthis_post_metabox::save_post function adds a meta item every time the post_save action is run. The problem stems from this section of code lines 54 through 62 of addthis_post_metabox.php

$custom_fields = get_post_custom($post_id);
if (! isset ($custom_fields['addthis_exclude'][0])  )
{
    add_post_meta($post_id, 'addthis_exclude', 'true');
}
else
{
    update_post_meta($post_id, 'addthis_exclude', 'true' , $custom_fields['addthis_exclude'][0]  );
}

From what I’ve found the problem is that when the new revision of the post that also triggers the save_post action has no meta so it triggers the add_post_meta section of the code which then uses wp_is_post_revision which returns the parent post id to have the meta applied to it and since add_post_meta doesn’t have the $unique parameter set as true it adds a duplicate meta value to the parent post.

Since this meta key is supposed to be unique and only has one value I found that changing the code above to this code fixed the problem for me.

if( ! update_post_meta($post_id, 'addthis_exclude', 'true' ) )
    add_post_meta( $post_id, 'addthis_exclude', 'true', true );

http://wordpress.org/extend/plugins/addthis/