default_unless broken example?

gistfile1.txt

# /backups/attributes/client.rb
# Jankily set a random time between midnight and 6am
hours = rand(6)
minutes = rand(59)
minutes = "0#{minutes}" if minutes < 10
random_time = "0#{hours}:#{minutes}"
default_unless['backups']['start_time'] = "everyday at #{random_time}"
default['backups']['extra_includes'] = []
default['backups']['extra_excludes'] = []
default['backups']['external_backup_user'] = 'external-backup'
default['backups']['external_backup_host'] = 'backups.marsdd.com'
default['backups']['external_backup_directory'] = "/var/external-backup/backups/#{node['ipaddress']}/"

# I expect the default_unless statement above to only set a new random time if there isn't already a
# key value pair for node['backups']['start_time'].  It seems to reset it on every chef run instead

# /backups/recipies/client.rb
template "/etc/backup.d/90.rdiff" do
    source "backup.d/90.rdiff.erb"
    owner "root"
    group "root"
    mode "0600"
    variables   :extra_includes => node['backups']['extra_includes'], 
                :extra_excludes => node['backups']['extra_excludes'],
                :external_backup_user => node['backups']['external_backup_user'],
                :external_backup_host => node['backups']['external_backup_host'],
                :external_backup_directory => node['backups']['external_backup_directory'] 
                
end

# Relevant debug output
[Wed, 04 Jan 2012 12:12:06 -0500] DEBUG: Processing template[/etc/backupninja.conf] on varnish1.comms.marsdd.com
[Wed, 04 Jan 2012 12:12:06 -0500] INFO: Processing template[/etc/backupninja.conf] action create (backups::client line 32)
[Wed, 04 Jan 2012 12:12:06 -0500] DEBUG: Not storing cookbooks/backups/templates/default/backupninja.conf.erb, as the cache is up to date.
[Wed, 04 Jan 2012 12:12:06 -0500] DEBUG: Current content's checksum:  5ed8826f65ee9976e739f96bf2af57060ae8d8c547b50cc2471165ad4612189e
[Wed, 04 Jan 2012 12:12:06 -0500] DEBUG: Rendered content's checksum: 0903da725324a76d27b157c31793e45262b21f7448e4833450de2119176be020
[Wed, 04 Jan 2012 12:12:06 -0500] INFO: template[/etc/backupninja.conf] backed up to /var/lib/chef/etc/backupninja.conf.chef-20120104121206
[Wed, 04 Jan 2012 12:12:06 -0500] INFO: template[/etc/backupninja.conf] removed backup at /var/lib/chef/./etc/backupninja.conf.chef-20120104115536
[Wed, 04 Jan 2012 12:12:06 -0500] INFO: template[/etc/backupninja.conf] mode changed to 644
[Wed, 04 Jan 2012 12:12:06 -0500] INFO: template[/etc/backupninja.conf] updated content