Yes, that was the problem. I also found out this in the help manual
register_globals boolean
Tells whether or not to register the EGPCS (Environment, GET, POST, Cookie, Server) variables as global variables. You may want to turn this off if you don't want to clutter your scripts' global scope with user data. This makes the most sense when coupled with track_vars - in which case you can access all of the EGPCS variables through the $HTTP_ENV_VARS, $HTTP_GET_VARS, $HTTP_POST_VARS, $HTTP_COOKIE_VARS, and $HTTP_SERVER_VARS arrays in the global scope.
So the problem was, that this value was off.