Webpage Expired / POSTDATA Expired

[eluser]gscharlemann[/eluser]
I've setup a simple page that is populated with database information based on an item selected from a dropdown list. When you follow a link from the data to a detailed page everything works fine, but if I push the "back" button on my browser I get:

IE: Webpage Expired
Firefox: The page you are trying to view contains POSTDATA that has expired from the cache.

The item selected from the dropdown box is submitted via POST. How do I prevent this item from "expiring"?

The controller function is as follows:

Code:

function index() {
        $data['races'] = $this->race_model->get_races();
        $race_selected = $this->input->post('race');
        $data['race_selected'] = $race_selected;
        if(!empty($race_selected)) {
            $data['race_data'] = $this->race_model->get_race($race_selected);
        }
        $this->load->view('header');
        $this->load->view('raceresults', $data);
        $this->load->view('footer');
    }

Thanks for your help!