On an existing Drupal system I see a strange phenomenon; user names disappear from the admin/people page. I've disabled the realname module but still it happens. How to debug such an issue?
Edit: Additional Information
My admin theme is Seven, so I've added a code to print the options array:
function seven_form_user_admin_account_alter(&$form, &$form_state, $form_id) {
dpm($form['accounts']['#options']);
}
The result: The username fields contains the following typical information:
<a href="/user/322" title="View user profile." class="username"
xml:lang="" about="/user/322" typeof="sioc:UserAccount"
property="foaf:name" datatype=""> </a>