Interesting fact: right now I’ve got Medivh as a regular visitor and him also as a story visitor at the campfire — however, only one Medivh is actually displayed here, meaning there is no special version of him as a quest visitor, whereas previously in such cases, including both story tasks and timed events, you could have two instances of the same character visiting you (alright, there is often a special version of a merc for timed events, but I remember seeing two Branns — with identical portraits — as well).
I don’t own any other portraits for Medivh, apart from the basic one, so I cannot test what effect changing his portrait would have on this situation.