CSS Delivery Optimizer breaks Seven theme

I can confirm it Seven theme works without any problem!
If you have some troubles with Seven or another admin theme you can add additional css rules with custom module like this:

function CUSTOMMODULE_preprocess_html(&$variables) {
// Add conditional stylesheets for admin pages on admin theme.
  if (arg(0)=="admin") {
    // reference your current admin theme  
    $theme_path = drupal_get_path('theme', 'seven');
    // reference your own stylesheet    
    drupal_add_css(drupal_get_path('module', 'CUSTOMMODULE') . '/css/admin.css', array('weight' => CSS_THEME));
  }
}

just add two files and one directory CSS for you module:
CUSTOMMODULE.info
CUSTOMMODULE.module
css/admin.css

I have exactly the same behavior like giupenni, when the Administration theme is different to the Standard Theme (/admin/appearance).
The critical CSS should be different for different themes – or at least should only affect the Standard Theme.
(BTW: Thank you for the great work! :-)

This is the expected behaviour at the moment. You can specify what pages should this be applied to in Page specific settings. Alternatively, as develway suggested, you can include additional CSS as a workaround.