When you hide a node, you are not hiding its related nodes. This is not necessarily intuitive to all users.

Example:
If you have embedded (related) an image in an article, and you hide the article, the image is still available to whoever knows the direct URL, for instance by searching for it by its description.

I have mentioned this in the documentation page for node visibility as well:
http://ez.no/doc/ez_publish/technical_manual/4_0/concepts_and_basics/content_management/node_visibility

It can be assumed by the editor that the embedded content is hidden as well. The administration interface should somehow notify the editor that the related content is not hidden, for instance by displaying this status in the "Relations" block in the content/view/full page.