The reason this happens is that the menu implementation in LabVIEW uses the single hyphen to indicate a seperator. And LabVIEW simply uses a menu popup as UI element also for enum controls. It's debateble if this is a good choice or if they should rather have created an alternate menu implementation for enums, but it is definitely a good thing for normal menus. The hyphen enum item itself is a valid element of the enum but because of the UI implementation as normal menu displayed as a seperator and therefore not selectable. And changing it now is most likely not an option especially since there is a workaround with the alternate hyphen.