The commerce_product_attributes.module currently has a little bug for anonymous users. If you edit a line item via URL parameter (line_item_id) it works perfectly for registered and logged in users. For anonymous users the values in the order form are not correctly prefilled with their values.
The reason and a patch can be found here, which helped me a lot. So I'd like to share it for other Drupal Developers:
https://drupal.org/node/1929782
Feel free to leave a not if this was helpful for you. :)
