zend.ze1_compatibility_mode issue

On a Ubuntu 9.04 system when I run: "drush status" in a working drupal directory I get the following error:

Fatal error: Cannot clone object of class PDO due to 'zend.ze1_compatibility_mode' in /usr/local/lib/drush/includes/environment.inc on line 835
Drush command could not be completed. [error]

I have set zend.ze1_compatibility_mode to on and off but get the same error each time. The line that it is complaining about is:
$db = new PDO($constr, $creds['user'], $creds['pass']);

I verified the parameters and to the best of my knowledge all they are correct.