Can't upgrade from 6.27 to 6.29 - Won't retrieve latest stable build from Drupal

When trying to upgrade the base postmaster install from Drupal 6.27 to 6.29, it should automatically download the latest stable branch (which is 6.29).

I've tried on two separate machines, and it will download 6.27 as the latest stable release when upgrading Aegir, and on a new install.

The commands I ran as the Aegir system user when doing the upgrade:
export OLD_AEGIR_DIR=/var/aegir/hostmaster-6.x-1.11
export AEGIR_VERSION=6.x-1.11
export AEGIR_DOMAIN=aurora.energetica.com.au
cd $OLD_AEGIR_DIR
drush hostmaster-migrate $AEGIR_DOMAIN $HOME/hostmaster-$AEGIR_VERSION

The output is as follows:
This command will operate the following changes in your system:

1. verify the server and the hostmaster site (provision-verify)
2. verify the new platform (which will download it if missing)
3. stop the queue (hosting-pause)
4. attempt a migration to the new platform (provision-migrate)
5. start the queue (hosting-resume)

We are making the following assumptions:
* you have read UPGRADE.txt
* you are executing this script as your "aegir" user

Do you really want to proceed with the upgrade? (y/n): y
Project information for drupal retrieved. [ok]
drupal downloaded from http://ftp.drupal.org/files/projects/drupal-6.27.tar.gz. [ok]
hostmaster cloned from http://git.drupal.org/project/hostmaster.git. [ok]
Checked out tag 6.x-1.11. [ok]
Found makefile: hostmaster.make [ok]
Project information for admin_menu retrieved. [ok]
Project information for openidadmin retrieved. [ok]
Project information for install_profile_api retrieved. [ok]
Project information for jquery_ui retrieved. [ok]
Project information for modalframe retrieved. [ok]
admin_menu downloaded from http://ftp.drupal.org/files/projects/admin_menu-6.x-1.8.tar.gz. [ok]
openidadmin downloaded from http://ftp.drupal.org/files/projects/openidadmin-6.x-1.2.tar.gz. [ok]
install_profile_api downloaded from http://ftp.drupal.org/files/projects/install_profile_api-6.x-2.1.tar.gz. [ok]
jquery_ui downloaded from http://ftp.drupal.org/files/projects/jquery_ui-6.x-1.3.tar.gz. [ok]
modalframe downloaded from http://ftp.drupal.org/files/projects/modalframe-6.x-1.6.tar.gz. [ok]
jquery_ui downloaded from http://jquery-ui.googlecode.com/files/jquery.ui-1.6.zip. [ok]
Backed up site up to /var/aegir/backups/aurora.energetica.com.au-20131127.123801.tar.gz. [success]
Created auroraenergeti_0 database [success]
Executing hosting_site_update_6009 [success]
'all' cache was cleared [success]
Finished performing updates. [ok]
The following updates are pending:

Is there an override variable to update the core version, or where does this need to be updated (Drupal's hosting end, or a make file somewhere in Aegir) ?