I did it, but it is not changed.
The username in PhpBB for example is: [ex]hello ; [ex]hello1 and in WP is: exhello and exhello1
The same happens to uppercase, changed in lowercase, for example: [ex]Luca in exluca
This is the part of code that I modifyed:
function wpb_get_username($count = 0)
$new_username = htmlspacialchars($user->data['username']);
if($count > 0)
$new_username .= (string)$count;
$new_username = wpb_get_username($count);
Maybe I must modify formatting.php, the sanitize_user function? Which are the risks if I'm going to insert a simply htmlspecialchars?