Rails - Oct 2009 - About transaction

I updated my rails from 2.0.2 to 2.3.4 yesterday. Then I found something
strange. I write transaction use ActiveRecord::Base.transaction block
like below:

  def action_name
    begin
     ActiveRecord::Base.transaction do
       object1.destroy
       object2.save!
     end
      render :json => {:success => true}.to_json,:layout=>false
    rescue Exception => exc
      render :json => {:success =>
false,:errors=>exc.message}.to_json,:layout=>false
    end
  end

It works better at 2.0.2, but the transaction did no work at 2.3.4. If
the object2.save! faile and raise exception, the transaction did not
rollback.

Is there some setting or config I must edit?
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