I'm seeding the RE with
<input type="hidden" name="artist_credit.names.0.name" value="Person1 and Person2">
<input type="hidden" name="mediums.1.track.0.name" value="Raga Jhinjoti">

On the first page of the RE we change the artist to a proper artist credit, Person1 "&" Person 2.
Moving to the tracklist, the artist column lists the original value, and not the correctly changed artist credit. We're not adding any mediums.n.track.m.artist_credit.names.x.name fields.
If you ignore these, hoping the release artist will be copied in, the missing entity screen kicks in.

I would expect the tracklist artist to be copied from the release artist always, not taken from the seeded value.