if you create a fresh new contact form in CMS, do not save it, add some form fields, do not save it, and delete the page. Then, the created form fields in the MySQL table `EditableFormFields` have `ParentID` == 0. They are not assigned to any page, cannot be deleted from CMS.
P.S. There's more of weird behaviour of the FieldEditor:
- remove some fields and go to another page. No 'Unsaved Changes' dialog is shown and you can jump to another page directly.
- add some new fields, go to another page and choose 'Discard changes' in the 'Unsaved Changes' dialog. When you return, you see, that changes has not been discarded (i.e., the added fields are still there)
- 'Cancel draft changes' function (aka rollback), does not work.