user_save regenerates the session even when current user != edited user.

Still applies to 5.x and even 6.x, but needs to be committed to HEAD and backported. Attached is the 6.x version. It is a straightforward update and looks good, so marking RTBC.

this bug affects all tests that'll try so do something as the root user admin.
this (example) test gives WSOD due to this bug.

class UserRootAdminLoginTestCase extends DrupalWebTestCase {
  function getInfo() {
    return array(
      'name' => t('Login as root admin'),
      'description' => t('Tries to login as root admin.'),
      'group' => t('User')
    );
  }

  /**
   * Try logging in as root administrator
   */
  function testRootAdminLogin() {
    // generate a password for the user
    $password = user_password();
    $root_admin = user_save(user_load(1), array('pass' => $password));

    // Add the raw password so that we can log in as this user.
    $root_admin->pass_raw = $password;

    // login as the root administrator
    $this->drupalLogin($root_admin);
  }
}

Committed to CVS HEAD. Updating version to Drupal 6.

The original patch works for Drupal 6, but I generated one from Drupal 6 because we really need this to make tests work.

Looks good, committed to 6.x, thanks!