I don't think that's a bug. a map id is not the same as a bookmark.
It originally (30+ years ago) was usually provided by the develper, and was a human-readable text paired with the map number.. The developer used to provide it because the number was created by the developer, and they provided the human-readable text so the author knew which screen/field/etc the number was associated with.
Later, the author sometimes created both the map number and map id and provided that list to the developer so they could make the apprpriate changes to the program.
I do rather like your idea of using a bookmark as a map id, but that would be a feature request, in my opinion.
There might be a problem if you don't ensure your bookmarks are unique across your entire project though. But I haven't used CSH for such a long time I'm not sure on that point. At best, someone might get confused if two map numbers have the same map id (which feature does the map number relate to?); or, your csh stops working or returns the wrong result for those calls.
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