PHP5 (5.3.3 in this case) may break in very supprising ways if the Memcached configured as a session handler goes awry.
In my case there was a webserver (Apache2 + mod_php5) w/ two memcached configured as session handler. One of those memcached got stuck and didn’t properly reply to request. This shouldn’t happen but whats even worse was that PHP5 just “died” with the following error in the syslog:
vs-www-s01 suhosin: ALERT - zend_mm_head corrupted at 0x7fc2f41a2090 (attacker ‘10.1.2.3’, file ‘/var/www/index.php’)This resulted in empty pages delivered to the browser.
After fixing the memcached everything was fine again.