My blogs are bugged because a filter seems to not work in your plugin.
That one should replace %s for the addthis:url and addthis:title but doesn't make the job...
addthis_social_widget.php: (line 1511)
$custom = preg_replace( '/<\s*div\s*/', '<div %s ', $options['below_custom_string'] );
$below = apply_filters('addthis_below_content', $custom); // Bugged