Weird border differences, when using conditional card and entity filter card in the same vertical stack

I have a quite thorough card, that I use to manage multiple media players in my house.
The main purpose is to autohide card that are not relevant, for instance:

  1. Hide Sonos players that are grouped with others, for this I use entity-filter
  2. Hide Apple TV card, when the linked Sonos TV speaker is playing music.

A simplied version of the code is as follows:

type: vertical-stack
title: Media
cards:
  - type: conditional
    conditions:
      - entity: media_player.living_room_tv
        state: playing
    card:
      type: custom:mini-media-player
      group: true
      artwork: material
      source: icon
      sound_mode: icon
      entity: media_player.living_room_tv
      info: short
      name: Living Room
  - type: conditional
    conditions:
      - entity: media_player.living_room_tv
        state_not: playing
    card:
      type: entity-filter
      entities:
        - type: custom:mini-media-player
          entity: media_player.living_room
  - type: entity-filter
    entities:
      - type: custom:mini-media-player
        entity: media_player.office
        state_filter:
          - attribute: group_members
            operator: regex
            value: ^..media_player.office[^_]

Why is it I get heavy borders on the entity-filter card, where it should preferably look more like the top conditional card?

image

It is the same if I use the custom stack-in-card. But I guess the issue could also be with the mini-media-player.