Account for posts added by thread expansion when marking read from index.

src/Monitoring/UnreadIndex.coffee

@@ -94,10 +94,7 @@ UnreadIndex =
 
   markRead: ->
     thread = Get.threadFromNode @
-    if Index.enabled
-      lastPost = Index.lastPost(thread.ID)
-    else
-      lastPost = 0
+    lastPost = if Index.enabled then Index.lastPost(thread.ID) else 0
     thread.posts.forEach (post) ->
       if post.ID > lastPost and !post.isFetchedQuote
         lastPost = post.ID