There's currently nothing in the codebase which prevents a user from inviting SYSTEM and then joining with that name.
Although it'll push a notification to say that someone did so, that notification won't be visible for anyone who joins afterwards. The user will then be able to push what appear to be system messages (i.e. they'll be purple and from SYSTEM).
Need to adjust the backend to prevent SYSTEM from being invited, or from joining as it's a reserved name.