I have the same issue. I need to display date in format: “M yy”, so I set Save format as “M yy” and Display format “dd/mm/yy” (default), but after update value isn’t displayed in input field. I can get this value in front-end and it is in right format, so everything works okay, except displaying saved value in backend.
I can see entered value after update only if Save format is “yymmdd”.