I've added the value <add key="CMSEnsureSafeUserNames" value="false" /> to the web.config on a v5.5.4248 R2 site, and it's either not taking, or the setting doesn't do what I think.

From CMS Desk / Administration / Users / Edit, trying to edit a username, if i add a space, and hit OK, it still displays the message

Please enter valid user name. The user name can contain only alphanumeric characters and some of special characters (_, -, ., @, \).

My understaning of CMSEnsureSafeUserNames was that, if set to false, it would allow anything at that point. Is that correct?

If so, any ideas why it's not taking? I saved the web.config which should have reset things as they were, and for safe measure, restarted the site in IIS and did Restart Application under Site Manager.