Setting an Optional YesNo Property to Maybe seems to be broken

(Bug, Closed -> Fixed, Priority: High, Test Status: No automated tests yet , Reported By Justin du Coeur, )
Editor
Summary: See the In Game property in A Respectful Calm. I am trying to set that to Maybe on Character, but it is stubbornly remaining No.
Not clear whether this is only in the Advanced Editor, but it might be. Maybe a regression from fixing the ExactlyOne YesNo in the Thing editor, but I'm not clear how that might be.