diff --git a/synapse/handlers/receipts.py b/synapse/handlers/receipts.py
index 4911a1153519..9fe980e72a94 100644
--- a/synapse/handlers/receipts.py
+++ b/synapse/handlers/receipts.py
@@ -267,6 +267,10 @@ async def get_new_events_as(
         )
 
         # Then filter down to rooms that the AS can read
+        # TODO: This doesn't seem to honour an appservice's registration of room or
+        #   namespace aliases. For instance, if an appservice registered a room namespace
+        #   that matched this room, but it didn't have any members in the room, then that
+        #   appservice wouldn't receive the read receipt.
         events = []
         for room_id, event in rooms_to_events.items():
             if not await service.matches_user_in_member_list(room_id, self.store):
diff --git a/synapse/handlers/typing.py b/synapse/handlers/typing.py
index 662ea59d420c..7290eecfa1e2 100644
--- a/synapse/handlers/typing.py
+++ b/synapse/handlers/typing.py
@@ -481,6 +481,11 @@ async def get_new_events_as(
             for room_id in handler._room_serials.keys():
                 if handler._room_serials[room_id] <= from_key:
                     continue
+
+                # TODO: This doesn't seem to honour an appservice's registration of room or
+                #   namespace aliases. For instance, if an appservice registered a room namespace
+                #   that matched this room, but it didn't have any members in the room, then that
+                #   appservice wouldn't receive the typing event.
                 if not await service.matches_user_in_member_list(
                     room_id, handler.store
                 ):