theme/module destination confusion

In a multi-site situation.
With all themes installed in sites/all/themes and modules installed in the individual sites/*/modules directories, running:

drush update

from within a specific multi-site root will properly update those modules which are local to the site; however, when attempting to update themes located in site/all/themes there is an error:

...
Module ad_blueprint path is not available, perhaps the module is     [error]
enabled but has been deleted from disk.
Backups were saved into the directory                                [ok]
/usr/local/www/drupal6-cvs/backup/modules/20091220130633.
Cache cleared.
An error occurred at function : drush_core_cache_clear               [error]
An error occurred at function : drush_pm_updatecode                  [error]
An error occurred at function : drush_pm_update                      [error]
[Exit 1 ]

I've started to trace the code; but I'm not familiar.