Load thread if requested thread isn't loaded yet.

common/static/coffee/src/discussion/discussion_router.coffee

@@ -51,6 +51,15 @@ if Backbone?
 
     showThread: (forum_name, thread_id) ->
       @thread = @discussion.get(thread_id)
+      if !@thread
+        callback = (thread) =>
+          @thread = thread
+          @renderThreadView()
+        @retrieveSingleThread(forum_name, thread_id, callback)
+      else
+        @renderThreadView()
+
+    renderThreadView: () ->
       @thread.set("unread_comments_count", 0)
       @thread.set("read", true)
       @setActiveThread()
@@ -97,3 +106,21 @@ if Backbone?
         complete: =>
           $('.forum-content').fadeIn(200).find('.thread-wrapper').focus()
       )
+
+    retrieveSingleThread: (forum_name, thread_id, callback) ->
+      DiscussionUtil.safeAjax
+        url: DiscussionUtil.urlFor('retrieve_single_thread', forum_name, thread_id)
+        success: (data, textStatus, xhr) =>
+          callback(new Thread(data['content']))
+        error: (xhr) =>
+          if xhr.status == 404
+            DiscussionUtil.discussionAlert(
+              gettext("Sorry"),
+              gettext("The thread you selected has been deleted. Please select another thread.")
+            )
+          else
+            DiscussionUtil.discussionAlert(
+              gettext("Sorry"),
+              gettext("We had some trouble loading more responses. Please try again.")
+            )
+          @allThreads()

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

@@ -22,12 +22,6 @@ if Backbone?
       if @mode not in ["tab", "inline"]
         throw new Error("invalid mode: " + @mode)
 
-      # Quick fix to have an actual model when we're receiving new models from
-      # the server.
-      @model.collection.on "reset", (collection) =>
-        id = @model.get("id")
-        @model = collection.get(id) if collection.get(id)
-
       @createShowView()
       @responses = new Comments()
       @loadedResponses = false