I just discovered that through a button embedded Smiley Pics (e.g. http://www.mydomain.com/sites/all/libraries/ckeditor/plugins/smiley/imag...) have the absolute URL and not the relative path like "sites/all/libraries/ckeditor/plugins/smiley/images/thumbs_up.gif".
This isn't optimal, because in the case of content development under a subdomain or other domain the picture link gets lost, when the domain changes (e.g. site is going live).