Volumes override doesn't work

[OnkelTem]

I have both docker-compose.yml and its override file. The essential part of the content is:

docker-compose.yml:

version: "3"
services:
  web:
    volumes:
      - "../app:/var/www/drupal:ro"

docker-compose.override.yml:

version: "3"
services:
  web:
    volumes:
      - "../app:/var/www/drupal:rw"
      - "./environments/local/data/composer:/home/developer/.composer:rw"

For some reason the override for ../app doesn't work - it is mounted in ro mode. But if comment out the second line (- "./environments/local/data/composer:/home/developer/.composer:rw") all of a sudden it starts seeing the override and works correctly. I don't see any logic in this behavior. Any ideas?

[shin-]

It's a bug with our merging method. Thank you for reporting it.

In the meantime, you can use the expanded volume notation with the 3.2 format which shouldn't be affected by this issue: https://docs.docker.com/compose/compose-file/#long-syntax-3

[ozmad]

I can't tell if I hit this bug but as a workaround (unintentionally) I mapped the volume to a different target file and started the container, then I stopped it, revert the volume mapping to the original one and the problem was fixed.
Voodoo is your friend.

[FelixBenning]

My overriding docker-compose.yml mounts the entire project folder (devcontainer). My original docker-compose.yml only mounts the configuration folder as ro. When I try to edit configuration files it errors as read-only.

I would have expected that the overriding mount would trump the read-only mount even though it is wider than the config only mount. Is this desired behavior?