Directory should use the alias or server information to join the room

[turt2live]

Just joining through room_id is not going to work

[bwindels]

OOI, why doesn't join with room id work?
Edit: Ah there's a comment why that is in the room directory code:

        // It's not really possible to join Matrix rooms by ID because the HS has no way to know
        // which servers to start querying. However, there's no other way to join rooms in
        // this list without aliases at present, so if roomAlias isn't set here we have no
        // choice but to supply the ID.