Bot name ?

[piratos]

Have you a bot name like w3c_validator or googlebot ?

Some sites must make two redirects to check some ability with javascript and write internal vars in php.

you detect this and follow, but you should do not - that was only for real users.

Bots like

$config['bots']=array('w3c_validator','googlebot','msnbot','slurp','gigabot','scrubby','robozil​a','nutch','ia_archiver','baiduspider','yahoo-mmcrawler','psbot','asterias','yahoo-blogs','SeitenReport');

are disabled automatically for redirects and so it was a good idea to set your name is this method.