Prevent name collisions on form value flattening?
While it's good practice to use unique field names in your form, you can use the #tree property to preserve the group nesting of parent -> same child name there.

$form['#tree'] = TRUE;


That will preserve the nesting of group -> field values in the form $form_state['values'] so instead of being flattened it will be

$form_state['values']['details']['admin'] = 'foo';


and

$form_state['values']['more_details']['admin'] = 'bar';