Ruby1.9 and ActiveRecord

I wanted to switch my app from ruby 1.8 to 1.9 but I notice ar-extensions' ActiveRecord#import takes longer. The code to demonstrate it is attached. There is no significant time difference in both variations in ruby 1.8 (I used fastercsv for 1.8). It looks like 1.9 issue, but first of all I'd appreciate if somebody can confirm this behavior

Thanks in advance.
-andre

------ test_ar.rb -----
require 'ar-extensions'
require 'csv'

ActiveRecord::Base.establish_connection :adapter => 'sqlite3', :dbfile => ':memory:'
ActiveRecord::Schema.define do
  create_table 'jobs' do |t|
    t.column :xid, :integer
    t.column :user, :string
    t.column :time, :time
    t.column :duration, :integer
    t.column :machine, :string
    t.column :command, :string
  end
end

# This one is slow. Notice local variable "job"
job = Class.new ActiveRecord::Base do
  set_table_name 'jobs'
end

# This one is fast. Notice constant "Job"
#Job = Class.new ActiveRecord::Base do
# set_table_name 'jobs'

#end
#job = Job

data = CSV.read "data.csv", :headers => false
job.import %w{ xid user time duration machine command }, data, :validate => false

# Fast one (with constant Job)
[lwe1:fx] time ruby19 test_ar.rb
-- create_table("jobs")
   -> 0.0701s
6.349u 0.231s 0:06.97 94.2% 0+0k 0+0io 0pf+0w

# Slow one (with local variable job)
[lwe1:fx] time ruby19 test_ar.rb
-- create_table("jobs")
   -> 0.0647s
27.533u 0.270s 0:28.08 99.0% 0+0k 0+0io 0pf+0w

···

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