Reported in forum by "---finder" http://forum.joomla.org/viewtopic.php?f=728&t=861042

Steps to reproduce the issue

Create a new user on front-end with username that starts with a non-breakable space. It does not matter if you use alpha, numeric or alphanumeric characters in the username.

To create a non-breakable space:
on Windows: ALT+255
on Apple OSX: [Option] + [Space]
on Debian Linux: [Control] + [Shift] + [U] + 00A1

Expected result

Expected error: "Registration failed: Please enter a valid username. No space at beginning or end, at least 2 characters and must not contain the following characters: < > \ " ' % ; ( ) &"

Actual result

Username starting with space has been created & the following message is displayed:
"Message
Your account has been created and an activation link has been sent to the email address you entered. Note that you must activate the account by clicking on the activation link when you get the email before you can login."

System information (as much as possible)

Additional comments

This issue is probably related with http://issues.joomla.org/tracker/joomla-cms/4481
If so, please merge.