Index: modules/user/user.module
===================================================================
RCS file: /cvs/drupal/drupal/modules/user/user.module,v
retrieving revision 1.1188
diff -u -r1.1188 user.module
--- modules/user/user.module	30 Jul 2010 02:47:28 -0000	1.1188
+++ modules/user/user.module	2 Aug 2010 11:15:32 -0000
@@ -574,7 +574,7 @@
  * Verify the syntax of the given name.
  */
 function user_validate_name($name) {
-  if (!$name) {
+  if (strlen(trim($name)) == 0) {
     return t('You must enter a username.');
   }
   if (substr($name, 0, 1) == ' ') {
@@ -973,6 +973,7 @@
     '#default_value' => (!$register ? $account->name : ''),
     '#access' => ($register || ($user->uid == $account->uid && user_access('change own username')) || $admin),
     '#weight' => -10,
+    '#validated' => TRUE,   // This is so user_validate_name() can handle the 'required' validation.
   );
 
   $form['account']['mail'] = array(
Index: includes/install.core.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/install.core.inc,v
retrieving revision 1.26
diff -u -r1.26 install.core.inc
--- includes/install.core.inc	30 Jul 2010 01:59:14 -0000	1.26
+++ includes/install.core.inc	2 Aug 2010 11:15:33 -0000
@@ -1638,6 +1638,7 @@
     '#required' => TRUE,
     '#weight' => -10,
     '#attributes' => array('class' => array('username')),
+    '#validated' => TRUE,   // This is so user_validate_name() can handle the 'required' validation.
   );
 
   $form['admin_account']['account']['mail'] = array('#type' => 'textfield',