case custom field using wysiwyg fails to load

create a custom data set for cases
create a field of type note, with the wysiwyg editor option enabled
create a case
in the manage case screen, open the custom set and click edit

instead of the modal popup opening to allow editing, the fields open in the panel and are uneditable. the wysiwyg field is displayed as a textarea box. and console reports the editor instance is not defined.