drush cron runs twice

I think the drush_tools_cron() callback is being mistaken for a hook_cron implementation.

jmorahan@jmorahan-laptop:/var/www/drupal$ drush watchdog delete all
Deleted 2 rows.
jmorahan@jmorahan-laptop:/var/www/drupal$ drush cron
Cron run successfully.
Cron run successfully.
jmorahan@jmorahan-laptop:/var/www/drupal$ drush watchdog show
  Date                  Severity        Type    Message                                                 User
  ----                  --------        ----    -------                                                 ----
  22 Jun 2007 - 8:35pm  warning         cron    Attempting to re-run cron while it is already running.  Anonymous
  22 Jun 2007 - 8:35pm  notice          cron    Cron run completed.                                     Anonymous