Using flashdata after redirect?

Have you tried

PHP Code:

var_dump($_SESSION); 


After setting it?

PHP Code:

$this->session->set_flashdata('message', 'test');
var_dump($_SESSION);
exit;
redirect('login', 'refresh'); 


Is the message available in the $_SESSION array?

I checked this and yes, the message is available in the $_SESSION array:

Code:

array (size=3)
 '__ci_last_regenerate' => int 1447806257
 'message' => string 'Update successful.' (length=18)
 '__ci_vars' =>
   array (size=1)
     'message' => string 'new' (length=3)

This was the dump before the redirect.

Is there an AJAX request? Maybe it somehow captures and clears the flashdata before the redirection?

A side note:
When AJAX is called by jQuery
headers["X-Requested-With"] = "XMLHttpRequest";
is done automatically, but in other cases this header might be forgotten.

No, there is no AJAX request. It is a normal form submission (POST request).