Backup task creates incomplete backup

Even though the Backup task log reports a failure a .tar.gz backup file is created.
This file is an incomplete backup and its existence could cause an admin to erroreously believe they have a valid backup.

The .tar.ga file should be removed upon a failure.

Task starts processing
Running: /usr/bin/php /var/aegir/drush/drush.php --root='/var/aegir/platform/drupal-6.15' 'provision' 'backup' 'example.com' --backend
Drush bootstrap phase : _drush_bootstrap_drush()
Drush bootstrap phase : _drush_bootstrap_drupal_root()
Loading drushrc "/var/aegir/platform/drupal-6.15/drushrc.php" into "drupal" scope.
Initialized Drupal 6.15 root directory at /var/aegir/platform/drupal-6.15
Found command: provision backup
Initializing drush commandfile: drush_make
Initializing drush commandfile: drush_make_d_o
Initializing drush commandfile: provision_apache
Undefined index: base_url
Initializing drush commandfile: provision_drupal
Initializing drush commandfile: provision_mysql
Undefined index: db_url
Including /var/aegir/.drush/provision/platform/backup.provision.inc
Including /var/aegir/.drush/provision/db_server/backup.provision.inc
Drush bootstrap phase : _drush_bootstrap_drupal_site()
Initialized Drupal site example.com at sites/example.com
Loading drushrc "/var/aegir/platform/drupal-6.15/sites/example.com/drushrc.php" into "site" scope.
Drush bootstrap phase : _drush_bootstrap_drupal_configuration()
Generating mysql dump for example.com.
mysqldump --defaults-file=/dev/fd/3 -rsites/example.com/database.sql site_393
Adding sites directory to /var/aegir/backups/example.com-20100223.181804.tar.gz
tar -C /var/aegir/platform/drupal-6.15/sites/example.com -p -c -z -f /var/aegir/backups/example.com-20100223.181804.tar.gz .
Could not back up sites directory for drupal
An error occurred at function : drush_provision_drupal_provision_backup
Deleted mysql dump from sites directory
Changes for drush_provision_mysql_pre_provision_backup module have been rolled back.
Command dispatch complete
Timer 'page' is 9.221 sec.
An error occurred at function : drush_hosting_hosting_task
Changes for drush_hosting_hosting_task module have been rolled back.
Command dispatch complete
Timer 'page' is 11.64 sec.