The changes to the /admin/includes/header.php file from ZC v1.5.1 to v1.5.3 appear to be downwardly compatible (there was no change from v1.5.2 to v1.5.3) and, it turns out, it's the v1.5.3 (modified) version of that file that's in the /YOUR_ADMIN/includes/header.php file that is part of this plugin's distribution.

I'll update the plugin's distribution file to identify that core-file overwrite in the readme.html and remove the redundant directories.