Using a Multisite within external scripts redirects to home url

Hi,

I’m currently using an WP 3.6 updated WPMU with only one sub site.

In this version the include of WP in external files is fine, but after upgrading to WP 4.1 these files redirect to the home url.

Site: https://example.com
WP: https://example.com/wordpress
Script: https://example.com/script.php

Unexpected behavoir:
https://example.com/script.php => redirect => https://example.com/wordpress

AFAIS after the upgrade WP can’t find the $current_blog. The config.inc.php wasn’t touched.