There are many system preferences which can take multiple selections, for example: - ArticleRequestsMandatoryFields - ArticleRequestsMandatoryFieldsItemOnly - ArticleRequestsMandatoryFieldsRecordOnly - BatchCheckoutsValidCategories By default they may have no options selected. Once any selection is saved, you are then unable to save the system preference again with no selections. Use the 'Select all' button to effectively select none. Notice you are unable to save the system preference - it thinks there is 'nothing to save'. We should be able to save a system preference with no selections.
*** This bug has been marked as a duplicate of bug 31364 ***