docker-compose remote interpreter volumes

Here's my docker-compose.yml

version: '3'
services:

  # Main application
  app:
    restart: always
    build:
      context: ./containers/app/
      args:
        - SSH_PRIVATE_KEY
    env_file:
      - ./config/env/files/app.env
    volumes:
      - ./containers/app/bin/:/app/bin/
      - ./containers/app/src/:/app/code/src/
      - ./containers/app/config/:/app/config/
      - ./containers/app/config/postfix/main.cf:/etc/postfix/main.cf
      - ./.git/:/app/.git/
      - ./logs/app/:/app/logs/
      # the line below mounts the XXXX repository at /lib for development.
      # this should be commented out on any environment except dev
      - ./containers/app/lib/:/app/code/lib/
      - app_data:/app/data/
    depends_on:
      - postgres
    ports:
      - 8000:8000

  # Main database server
  postgres:
    build: ./containers/postgres/
    restart: unless-stopped
    env_file:
      - ./config/env/files/postgres.env
    volumes:
      - postgres_data:/var/lib/postgresql/data
    ports:
      - 5432:5432

volumes:
  postgres_data:
  app_data:

My Django app's static data ends up in `/app/data/static`, but any changes made to the static content from within the container (e.g. by Grunt process that watches on CSS/JS changes) isn't reflected outside the container, which makes me wonder if the volumes are even taking effect.

Or is there perhaps something which I'm missing with the run configuration?