I already figured out that safe_mode and magic_quotes got disabled at php 5.4.
If I try to enable log_error in the php.ini and after restarting the apache server I'll get a 500 (internal server) error.
Figured out too, that I need to disable the php_editor for the domain if I want to change things manually. But still, log_error should be still usable in php 5.4.
Someone knows why? If you need any logs or more information, just ask please.