Please ask your friend to complain, as this is a problem apparently unique to XC.
I agree it is ridiculous and most people I know who have expressed an opinion seem to be of the same view, though one member in particular disagrees with us and does want invisible reservations to be enforced (see
Voyager reservations - failing again!!)
If there are no reservations, then there are no reservations, and that should be the end of that. That's how other operators work!
I've only ever known XC enforce invisible reservations. A passenger travelling on a long distance journey could potentially be asked to move numerous times throughout their journey. Even on a short journey e.g. York-Sheffield you could be asked to move 3 times (once shortly after York, again at Leeds and again at Wakefield)