Class of alias nodes differs from class of anchor nodes in Psych

example.yaml

:original: &id001 2012-04-14 11:00:00 Z
:alias: *id001

irb

# Ruby 1.9.2-p290
require 'yaml'

from_syck = YAML.load_file("example.yaml")

from_syck[:original].class # => Time
from_syck[:alias].class    # => Time

require 'psych'
YAML::ENGINE.yamler = 'psych'

from_psych = YAML.load_file("example.yaml")

from_psych[:original].class # => Time
from_psych[:alias].class    # => String