If you add a hidden special field to a category menu table, the record is still displayed in the parentCategory field when hidden is set.
It should not be shown.
The hidden field is designed to stop records displaying on the front end of the site while a user edits them an prepares them for publishing in the CMS. CMSB still shows the hidden records in the Parent Category field in the CMS so that a user can set up the structure of the records as they'd like before publishing.
PHP Programmer - interactivetools.com