Index: app/controllers/messages_controller.rb
===================================================================
--- app/controllers/messages_controller.rb	(revision 16559)
+++ app/controllers/messages_controller.rb	(working copy)
@@ -34,16 +34,19 @@
   def show
     page = params[:page]
     # Find the page of the requested reply
+    replies_order = User.current.wants_comments_in_reverse_order? ? 'DESC' : 'ASC'
+    @replies = @topic.children.
+      includes(:author, :attachments, {:board => :project}).
+      reorder("#{Message.table_name}.created_on #{replies_order}, #{Message.table_name}.id #{replies_order}")
+
     if params[:r] && page.nil?
-      offset = @topic.children.where("#{Message.table_name}.id < ?", params[:r].to_i).count
+      offset = @replies.pluck(:id).index(params[:r].to_i)
       page = 1 + offset / REPLIES_PER_PAGE
     end
 
-    @reply_count = @topic.children.count
+    @reply_count = @replies.count
     @reply_pages = Paginator.new @reply_count, REPLIES_PER_PAGE, page
-    @replies =  @topic.children.
-      includes(:author, :attachments, {:board => :project}).
-      reorder("#{Message.table_name}.created_on ASC, #{Message.table_name}.id ASC").
+    @replies = @replies.
       limit(@reply_pages.per_page).
       offset(@reply_pages.offset).
       to_a
Index: test/integration/messages_test.rb
===================================================================
--- test/integration/messages_test.rb	(nonexistent)
+++ test/integration/messages_test.rb	(working copy)
@@ -0,0 +1,39 @@
+require File.expand_path('../../test_helper', __FILE__)
+
+class MessagesTest < Redmine::IntegrationTest
+  fixtures :projects, :users, :email_addresses, :user_preferences, :members,
+           :member_roles, :roles, :boards, :messages, :enabled_modules
+
+  def setup
+    message = Message.find(1)
+    assert_difference 'Message.count', 60 do
+      60.times do
+        message.children << Message.new(
+          :subject => 'Reply',
+          :content => 'Reply body',
+          :author_id => 2,
+          :board_id => 1)
+      end
+    end
+    @reply_ids = message.children.map(&:id).sort
+
+    log_user('jsmith', 'jsmith')
+  end
+
+  def test_show_with_pagination_should_ascending_order
+    post '/my/account', :pref => { :comments_sorting => 'asc' }
+    get '/boards/1/topics/1', :r => @reply_ids.last
+
+    assert !User.current.wants_comments_in_reverse_order?
+    assert_select 'span.pagination > ul.pages > li.current > span', text: '3'
+  end
+
+  def test_show_with_pagination_should_descending_order
+    post '/my/account', :pref => { :comments_sorting => 'desc' }
+    get '/boards/1/topics/1', :r => @reply_ids.last
+
+    assert User.current.wants_comments_in_reverse_order?
+    assert_select 'span.pagination > ul.pages > li.current > span', text: '1'
+  end
+
+end