I wonder if that's just HTML - normally multiple spaces get condensed to one. I'm not sure how to fix that easily. You could find everywhere a user name is being displayed and change spaces to , but that seems like a lot of places.
There's a function called fetch_musername() in includes/functions that gets the "marked up" user name, so if you changed that it would probably handle most places, but I know there are some places where it's just the bare user name.
In retrospect, the single-space thing is probably a good thing because having people with the same user name other than spacing could get confusing (but I'm sure you have your reasons for wanting to allow it).
My reasons are that I read the username of vBull with my java server, and people can have usernames with 2 spaces on the game, unfortunately they cannot on the forum, and that causes a conflict.