We have a drupal 7 website, getting about +50.000 unique visitors each day. For statistical purposes, we are logging the events on the site, and one of the items logged is the referrer $_SERVER['HTTP_REFERER']. However, this is only captured less then 4% of the time, for 96%, $_SERVER['HTTP_REFERER'] is NULL. I know that $_SERVER['HTTP_REFERER'] isn't a trustworthy item, but 4% seems extremely low to me! I wrote a seperate PHP testscript to capture and log $_SERVER['HTTP_REFERER'], and this one works flawless, and the referer is filled in each time, from each browser/system/location I've tried. The Drupal 7 installation runs on 2 apache nodes with an apache loadbalancer.
Any tips on what might cause $_SERVER['HTTP_REFERER'] to be removed?
