You can create users with spaces

[mudmin]

There is no validation on inserting new users in the database in the back end because you are the administrator so you can do what ever you want. You can add the validation script that is on the join.php form if you want it. There's also not technically a problem with spaces in a username.

Note that if we're using Input::get for grabbing the form information, that it is being sanitized against sql injections.