Sorting should keep trace of comment and like updates.

lms/static/coffee/src/discussion/content.coffee

@@ -439,6 +439,9 @@ if Backbone?
       @set('thread', @)
       super()
 
+    comment: ->
+      @set("comments_count", parseInt(@get("comments_count")) + 1)
+
     follow: ->
       @set('subscribed', true)
       @trigger "thread:follow"

lms/static/coffee/src/discussion/views/discussion_thread_list_view.coffee

@@ -10,6 +10,11 @@ class @DiscussionThreadListView extends Backbone.View
 
   initialize: ->
     @displayedCollection = new Discussion(@collection.models)
+    @collection.on "change", @reloadDisplayedCollection
+
+  reloadDisplayedCollection: =>
+    @displayedCollection.reset(@collection.models)
+
 
   # Because we want the behavior that when the body is clicked the menu is
   # closed, we need to ignore clicks in the search field and stop propagation.
@@ -96,10 +101,6 @@ class @DiscussionThreadListView extends Backbone.View
       @displayedCollection.comparator = @displayedCollection.sortByComments
     @displayedCollection.sort()
 
-  delay: (callback, ms) =>
-    clearTimeout(@timer)
-    @timer = setTimeout(callback, ms)
-
   performSearch: (event) ->
     if event.which == 13
       event.preventDefault()

lms/static/coffee/src/discussion/views/discussion_thread_view.coffee

@@ -62,7 +62,7 @@ class @DiscussionThreadView extends DiscussionContentView
       @$(".responses").append(view.el)
 
   addComment: =>
-    @model.trigger "comment:add"
+    @model.comment()
 
   toggleVote: (event) ->
     event.preventDefault()

lms/static/coffee/src/discussion/views/thread_list_item_view.coffee

 class @ThreadListItemView extends Backbone.View
   tagName: "li"
   template: _.template($("#thread-list-item-template").html())
+
   events:
     "click a": "threadSelected"
+
   initialize: ->
     @model.on "change", @render
     @model.on "thread:follow", @follow
     @model.on "thread:unfollow", @unfollow
-    @model.on "comment:add", @addComment
+
   render: =>
     @$el.html(@template(@model.toJSON()))
     if window.user.following(@model)