Course: Updated posts should be also ACKed

owl/course.py

@@ -174,8 +174,11 @@ def topic_index(sident: str, cident: str, tident: str, student_uid: Optional[int
                    topic=g.topic)
     )
 
-    if posts and (seen is None or seen < posts[-1].created):
-        form.ack_time.data = posts[-1].created
+    post_times = [p.created for p in posts] + [p.modified for p in posts if p.modified is not None]
+    if post_times:
+        last_post_time = max(post_times)
+        if seen is None or seen < last_post_time:
+            form.ack_time.data = last_post_time
 
     return render_template(
         'topic.html',