hiera deep merge won't

gistfile1.txt

[root puppet]# hiera -d -h users  -c /etc/puppet/hiera.yaml environment=production
DEBUG: Mon Mar 18 10:05:26 -0400 2013: Hiera YAML backend starting
DEBUG: Mon Mar 18 10:05:26 -0400 2013: Looking up users in YAML backend
DEBUG: Mon Mar 18 10:05:26 -0400 2013: Looking for data source production/common
DEBUG: Mon Mar 18 10:05:26 -0400 2013: Found users in production/common
/usr/lib/ruby/site_ruby/1.8/hiera/backend.rb:156:in `merge_answer': undefined method `deep_merge' for {"beast"=>{"v_ingroups"=>["one", "two"]}}:Hash (NoMethodError)
        from /usr/lib/ruby/site_ruby/1.8/hiera/backend/yaml_backend.rb:49:in `lookup'
        from /usr/lib/ruby/site_ruby/1.8/hiera/backend.rb:68:in `datasources'
        from /usr/lib/ruby/site_ruby/1.8/hiera/backend.rb:66:in `map'
        from /usr/lib/ruby/site_ruby/1.8/hiera/backend.rb:66:in `datasources'
        from /usr/lib/ruby/site_ruby/1.8/hiera/backend/yaml_backend.rb:16:in `lookup'
        from /usr/lib/ruby/site_ruby/1.8/hiera/backend.rb:182:in `lookup'
        from /usr/lib/ruby/site_ruby/1.8/hiera/backend.rb:179:in `each'
        from /usr/lib/ruby/site_ruby/1.8/hiera/backend.rb:179:in `lookup'
        from /usr/lib/ruby/site_ruby/1.8/hiera.rb:64:in `lookup'
        from /usr/bin/hiera:220