Playlists endpoint fields param dot separator no longer working

[kingosticks4]

For a long time my app has been using the dot separator syntax to specify specific fields in the response v1/playlists/{playlist_id} endpoint e.g.if I wanted the three fields "name,owner.id,type" I would do:

'https://api.spotify.com/v1/playlists/0rAgBTjDlOvxbsbGapLzDw?market=from_token&fields=name%2Cowner.id...'

Which should return:

{
  "name": "Battersea Choons!",
  "owner": {
    "id": "bob"
  },
  "type": "playlist"
}

However, things go wrong after the dot separator in "owner.id" and lately I actually get

{
  "name": "Battersea Choons!",
  "owner": {
    "id": "bob",
    "type": "user"
  }
}

If I use the bracket syntax instead e.g. "name,owner(id),type" then it works as I expect.

I say "lately" because this used to all work properly (or at least, work differently). Has something changed here?