Flashdata being set but can't be echoed

[eluser]ChazUK[/eluser]
I'm having a real problem here.

I've been trying to use the session->flashdata() functions because I can see a real use for them, but I can't seem to echo any of the data out on the next page.

Example
/anypage/

Code:

$this->ci->session->set_flashdata('referrer', uri_string());
redirect('/login/');

/login/

Code:

var_dump($this->session->flashdata('referrer'));

and it always comes out as bool(false).

I have looked in the DB and I can see that the stuff is being written as flashdata:new:referrer, but I can't access it on /login/.