Index: wp-includes/user.php
===================================================================
--- wp-includes/user.php	(revision 11300)
+++ wp-includes/user.php	(working copy)
@@ -85,7 +85,7 @@
 
 	$userdata = get_userdatabylogin($username);
 
-	if ( !$userdata || ($userdata->user_login != $username) ) {
+	if ( !$userdata ) {
 		return new WP_Error('invalid_username', sprintf(__('<strong>ERROR</strong>: Invalid username. <a href="%s" title="Password Lost and Found">Lost your password</a>?'), site_url('wp-login.php?action=lostpassword', 'login')));
 	}