It's indeed not possible to add standard fields via "Options > Tag Panel". I've decided to not allow adding multiple instances of one and the same field to the Tag Panel, to prevent confusion and assumptions about the priority of those fields (which becomes relevant as soon as you have multiple instances of the same field on the panel).
This is also the reason why those fields are not listed in the field list when adding a new field. And yes, if you're entering the standard field name manually, the OK button won't allow you to close the dialog.
I'm fine with the workaround of editing the *.ini field manually — in fact, I find it to be quite creative 
However, no promise is made whether this will work forever (though, I have no plans of breaking this).
Kind regards
— Florian