drush appears to not be respecting --no-backup My server has a great backup system in place.  I do not need additional backups dropped into my home directory.

Reading the drush docs gave me the impression that the --no-backup option, would instruct drush to not make a backup.

$ drush --version
drush version 4.5


When I update a module with the --no-backup option it seems to be ignored.

$ ls ~/
creds
$ drush dl drush --no-backup --yes
Would you like to back up your current drush version 4.5 to /home/username/drush-backups/unknown/20110823223228 and replace it with drush 4.5? (y/n): y
drush backed up to /home/username/drush-backups/unknown/20110823223228/drush  [ok]
Project drush (7.x-4.5) downloaded to                                [success]
/srv/www/_drupal_.example.org/drush.
Drush successfully updated to version 7.x-4.5.                       [success]
$ ls ~/
creds  drush-backups


Am I missing something obvious here?  I have tried changing the order of the parameters, but that doesn't seem to make any difference.
This is a Drush bug, and would best be raised in the issue queue.  By coincidence, someone recently posted this: http://drupal.org/node/1741108