clone doesn't rollback if failure during the final cache clear

Here's a few fragments of a provision-clone:

Running: /usr/share/drush/drush.php --old_uri='example.com' @example.com provision-deploy '/var/aegir/backups/example.com-20120619.082041.tar.gz' --backend 2>&1
The external command could not be executed due to an application error.
[...]
Running: /usr/share/drush/drush.php @example.com updatedb --backend 2>&1
Command dispatch complete
Peak memory usage was 68.95 Mo
[...]
Cleared all caches
Rebuilt node type cache
Rebuilt code registry
Rebuilt theme cache
Drush command terminated abnormally due to an unrecoverable error. Error: Cannot redeclare _menu_block_theme() (previously declared in /srv/aegir/platforms/drupal-7-build-2012.06.14-staging/sites/example.com/modules/contrib/menu_block/menu_block.admin.inc:10) in /srv/aegir/platforms/drupal-7-build-2012.06.14-staging/sites/example.com/modules/contrib/menu_block/menu_block.admin.inc, line 30
Removed unused clone site package
Changes made in drush_provision_drupal_pre_provision_clone have been rolled back.
Command dispatch complete
Peak memory usage was 26.72 MB
Command dispatch complete
Peak memory usage was 58.01 MB

Now of course that failure shouldn't happen in the first place and this is a programming error in the menu_block.module (i guess). But Aegir should nevertheless be able to recover fromt his, and rollback. The rollback, I think, should remove the created site because as things stand the site clone is created and is left lying around without being properly imported in the frontend.

So one of two things:

1. ignore that error
2. rollback by deleting the clone