Hi James
Thank you for your reply. Unfortunately the error is not on the field group editor page. It occurs within the editor view of a page where the fields should (or better: should not) be displayed. Sorry if that was not clear enough before.
I try to describe the situation again (hopefully a bit clearer than before):
The fields with the admin_only option are placed inside a layout field item using a single clone field. This layout field item (among other similar layout field items) are used on pages that use a specific page-template.
