Further clarify why membership events are not to be transferred
@@ -61,7 +61,11 @@ When the client requests to upgrade a known room to a known version, the server:
* ``m.room.join_rules``
* ``m.room.power_levels``
- Membership events should not be transferred to the new room.
+ Membership events should not be transferred to the new room due to technical limitations
+ of servers not being able to impersonate people from other homeservers. Additionally,
+ servers should not transfer state events which are sensitive to who sent them, such as
+ events outside of the Matrix namespace where clients may rely on the sender to match
+ certain criteria.
4. Moves any local aliases to the new room.
5. Sends a ``m.room.tombstone`` event to the old room to indicate that it is not intended
