Kill requests for loading responses when selecting another thread. This ensures that the thread you're viewing has the right responses loaded.

lms/static/coffee/src/discussion/discussion_router.coffee

@@ -26,6 +26,7 @@ if Backbone?
       @thread = @discussion.get(thread_id)
       @setActiveThread()
       if(@main)
+        @main.cleanup()
         @main.undelegateEvents()
 
       @main = new DiscussionThreadView(el: $(".discussion-column"), model: @thread)

lms/static/coffee/src/discussion/utils.coffee

@@ -71,7 +71,7 @@ class @DiscussionUtil
           params["loadingCallback"].apply(params["$loading"])
         else
           params["$loading"].loading()
-    $.ajax(params).always ->
+    request = $.ajax(params).always ->
       if $elem
         $elem.removeAttr("disabled")
       if params["$loading"]
@@ -79,6 +79,7 @@ class @DiscussionUtil
           params["loadedCallback"].apply(params["$loading"])
         else
           params["$loading"].loaded()
+    return request
 
   @get: ($elem, url, data, success) ->
     @safeAjax

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

@@ -23,10 +23,15 @@ if Backbone?
       @renderResponses()
       @
 
+    cleanup: ->
+      if @responsesRequest?
+        @responsesRequest.abort()
+
     renderResponses: ->
-      DiscussionUtil.safeAjax
+      @responsesRequest = DiscussionUtil.safeAjax
         url: "/courses/#{$$course_id}/discussion/forum/#{@model.get('commentable_id')}/threads/#{@model.id}"
         success: (data, textStatus, xhr) =>
+          @responsesRequest = null
           @$el.find(".loading").remove()
           Content.loadContentInfos(data['annotated_content_info'])
           comments = new Comments(data['content']['children'])