Migrations - very confusing

If I rename 001_do_step1.php to 001_do_step1.txt, it works.
Your example still generated the "duplicate field" error, because it calls $this->migration->currunt() twice!
I've got it working now with this code:

PHP Code:

    public function do_migrate()
    {
        $version = $this->migration->current();
        if (! $version) {
            show_error($this->migration->error_string());
            exit;            
        }
        echo 'Migration ' . $version . ' successful';
    } 


I'm still wondering how to do a roll-back. Each migration file has an "up" method and a "down" method. When is the "up" method called?