fixes #1680

app/models/forum_post.rb

@@ -8,6 +8,7 @@ class ForumPost < ActiveRecord::Base
   before_validation :initialize_updater
   before_validation :initialize_is_deleted, :on => :create
   after_create :update_topic_updated_at_on_create
+  after_update :update_topic_updated_at_on_update_for_orignal_posts
   after_destroy :update_topic_updated_at_on_destroy
   validates_presence_of :body, :creator_id
   validate :validate_topic_is_unlocked
@@ -95,6 +96,12 @@ class ForumPost < ActiveRecord::Base
     end
   end
 
+  def update_topic_updated_at_on_update_for_orignal_posts
+    if is_original_post?
+      topic.touch
+    end
+  end
+
   def update_topic_updated_at_on_destroy
     max = ForumPost.where(:topic_id => topic.id).maximum(:updated_at)
     if max