keep_flashdata bug? [urgent help needed]

[eluser]PoWah[/eluser]
I dont get whats wrong. On my local machine (windows) keep_flashdata works as expected - it keeps the data in session, but on the production server (linux) it does NOT keep the data :/
Tested with firefox on both. Can somebody explain what influences that behavior?

Code:

function bid()
{
    // ...
    $this->session->set_flashdata("cb", $confirm_data);
    redirect('auction/bid_confirm');
    // ...
}

function bid_confirm()
{
    // ...
    $confirm_data = $this->session->flashdata("cb");
    if (!$confirm_data)
    {
    redirect('');
    exit;
    }
    $this->session->keep_flashdata('cb');
    // ...
}