Suhosin is an advanced protection system for PHP installations. It was
designed to protect servers and users from known and unknown flaws in
PHP applications and the PHP core. Suhosin comes in two independent
parts,that can be used separately or in combination. The first part
is a small patch against the PHP core,that implements a few low-level
protections against bufferoverflows or format string vulnerabilities
and the second part is a powerful PHP extension that implements all
the other protections

http://www.hardened-php.net/suhosin/configuration.html#suhosin.simulation

When Suhosin runs in simulation mode,violations are logged as usual,but nothing is blocked or removed from the request.