diff --git a/synapse/handlers/room_member.py b/synapse/handlers/room_member.py
index 2f8782e522..8e7bbe9f75 100644
--- a/synapse/handlers/room_member.py
+++ b/synapse/handlers/room_member.py
@@ -89,7 +89,7 @@ class RoomMemberHandler(BaseHandler):
         duplicate = yield msg_handler.deduplicate_state_event(event, context)
         if duplicate is not None:
             # Discard the new event since this membership change is a no-op.
-            return
+            defer.returnValue(duplicate)
 
         yield msg_handler.handle_new_client_event(
             requester,
@@ -120,6 +120,8 @@ class RoomMemberHandler(BaseHandler):
                 if prev_member_event.membership == Membership.JOIN:
                     user_left_room(self.distributor, target, room_id)
 
+        defer.returnValue(event)
+
     @defer.inlineCallbacks
     def remote_join(self, remote_room_hosts, room_id, user, content):
         if len(remote_room_hosts) == 0:
@@ -187,6 +189,7 @@ class RoomMemberHandler(BaseHandler):
             ratelimit=True,
             content=None,
     ):
+        content_specified = bool(content)
         if content is None:
             content = {}
 
@@ -229,6 +232,12 @@ class RoomMemberHandler(BaseHandler):
                     errcode=Codes.BAD_STATE
                 )
 
+            same_content = content == old_state.content
+            same_membership = old_membership == effective_membership_state
+            same_sender = requester.user.to_string() == old_state.sender
+            if same_sender and same_membership and same_content:
+                defer.returnValue(old_state)
+
         is_host_in_room = yield self._is_host_in_room(current_state_ids)
 
         if effective_membership_state == Membership.JOIN:
@@ -247,8 +256,9 @@ class RoomMemberHandler(BaseHandler):
                 content["membership"] = Membership.JOIN
 
                 profile = self.hs.get_handlers().profile_handler
-                content["displayname"] = yield profile.get_displayname(target)
-                content["avatar_url"] = yield profile.get_avatar_url(target)
+                if not content_specified:
+                    content["displayname"] = yield profile.get_displayname(target)
+                    content["avatar_url"] = yield profile.get_avatar_url(target)
 
                 if requester.is_guest:
                     content["kind"] = "guest"
@@ -290,7 +300,7 @@ class RoomMemberHandler(BaseHandler):
 
                         defer.returnValue({})
 
-        yield self._local_membership_update(
+        res = yield self._local_membership_update(
             requester=requester,
             target=target,
             room_id=room_id,
@@ -300,6 +310,7 @@ class RoomMemberHandler(BaseHandler):
             prev_event_ids=latest_event_ids,
             content=content,
         )
+        defer.returnValue(res)
 
     @defer.inlineCallbacks
     def send_membership_event(
diff --git a/synapse/rest/client/v1/room.py b/synapse/rest/client/v1/room.py
index eead435bfd..2ebf5e59a0 100644
--- a/synapse/rest/client/v1/room.py
+++ b/synapse/rest/client/v1/room.py
@@ -152,23 +152,29 @@ class RoomStateEventRestServlet(ClientV1RestServlet):
         if state_key is not None:
             event_dict["state_key"] = state_key
 
-        msg_handler = self.handlers.message_handler
-        event, context = yield msg_handler.create_event(
-            event_dict,
-            token_id=requester.access_token_id,
-            txn_id=txn_id,
-        )
-
         if event_type == EventTypes.Member:
-            yield self.handlers.room_member_handler.send_membership_event(
+            membership = content.get("membership", None)
+            event = yield self.handlers.room_member_handler.update_membership(
                 requester,
-                event,
-                context,
+                target=UserID.from_string(state_key),
+                room_id=room_id,
+                action=membership,
+                content=content,
             )
         else:
+            msg_handler = self.handlers.message_handler
+            event, context = yield msg_handler.create_event(
+                event_dict,
+                token_id=requester.access_token_id,
+                txn_id=txn_id,
+            )
+
             yield msg_handler.send_nonmember_event(requester, event, context)
 
-        defer.returnValue((200, {"event_id": event.event_id}))
+        ret = {}
+        if event:
+            ret = {"event_id": event.event_id}
+        defer.returnValue((200, ret))
 
 
 # TODO: Needs unit testing for generic events + feedback
diff --git a/tests/rest/client/v1/test_rooms.py b/tests/rest/client/v1/test_rooms.py
index 4fe99ebc0b..6bce352c5f 100644
--- a/tests/rest/client/v1/test_rooms.py
+++ b/tests/rest/client/v1/test_rooms.py
@@ -259,8 +259,8 @@ class RoomPermissionsTestCase(RestTestCase):
         # set [invite/join/left] of self, set [invite/join/left] of other,
         # expect all 404s because room doesn't exist on any server
         for usr in [self.user_id, self.rmcreator_id]:
-            yield self.join(room=room, user=usr, expect_code=403)
-            yield self.leave(room=room, user=usr, expect_code=403)
+            yield self.join(room=room, user=usr, expect_code=404)
+            yield self.leave(room=room, user=usr, expect_code=404)
 
     @defer.inlineCallbacks
     def test_membership_private_room_perms(self):
diff --git a/tests/rest/client/v1/utils.py b/tests/rest/client/v1/utils.py
index 17524b2e23..3bb1dd003a 100644
--- a/tests/rest/client/v1/utils.py
+++ b/tests/rest/client/v1/utils.py
@@ -87,7 +87,10 @@ class RestTestCase(unittest.TestCase):
         (code, response) = yield self.mock_resource.trigger(
             "PUT", path, json.dumps(data)
         )
-        self.assertEquals(expect_code, code, msg=str(response))
+        self.assertEquals(
+            expect_code, code,
+            msg="Expected: %d, got: %d, resp: %r" % (expect_code, code, response)
+        )
 
         self.auth_user_id = temp_id