ItemFlag#HIDE_POTION_EFFECTS is an unnecessarily confusing name for an enum that also hides other things like the artist and name of a music disc and perhaps more.
On Paper, this enum is renamed to ItemFlag#HIDE_ITEM_SPECIFICS, which makes a lot more sense in my opinion.
Renaming an enum member is not that simple. Even the fork you're referring to just added a constant and deprecated the enum member.
If the enum member would be renamed it would break a lot of plugins. To some extend this could be handled with Commodore, but you can't override valueOf() of an enum.
The JavaDoc of this member could be improved to reflect current uses.