Fixed in the current ZIP.
This occurs for any articles with UTF-8 characters in the title when using vBulletin 4. It's really annoying how much different $relpath is from $scriptpath (this is a distinction between vB3 and 4 that's at the root of this problem).
If anyone needs this functionality immediately, download the ZIP again and replace vault/special_class_wiki.php and vault/special_plugins.php.