Hi All!
Just to sum this all up:
I've entered Sebastians short code of reproduction in the PHP bugtracker and then was notified that this had already been tracked:
http://bugs.php.net/bug.php?id=35995
This bureport confirms what I stated first: The way of specifying preg_match($string, $pattern, $matches = array()) is invalid, and the bug was that it worked in earlier versions - not that it stopped working now. Still a BC-break, but it seems that the PHP people don't mind about that. :-/
Best regards, Garvin