Docker compose fiware WireCloud data persistance not loaded from volume

I am using a docker container for my FiWare WireCloud. It is working properly but when I stop my container with docker compose down and restart it with docker compose up all my data are erased even if I specified a volume for the postgresql database and I have the following error:

ERROR:  relation "wirecloud_workspace" does not exist at character 370

If I want to make it work again, I have to recreate the whole database from scratch (initdb & createsuperuser)

What I would like to do is to be able to save my wirecloud data inside a volume and be able te backup it and reload it. Here is my current docker-compose.yml file in version 3:

version: '3.3'
services:

    iot-mongo:
        image: mongo:3.2
        ports:
         - "27017:27017"
        volumes:
            - ./data/mongo:/data/db

    orion:
      image: fiware/orion:1.9.0
      links:
        - iot-mongo
      ports:
        - "1026:1026"
      command: -dbhost iot-mongo


    nginx:
        restart: always
        image: nginx:1.13
        ports:
            - "80:80"
            - "443:443"
        volumes:
            - ./nginx/nginx.conf:/etc/nginx/nginx.conf:ro
            - ./nginx/sites-available:/etc/nginx/sites-available
            - ./letsencrypt/well-known:/www/letsencrypt
            - /etc/letsencrypt/:/etc/letsencrypt/
            - wirecloudwww:/var/www/static
            - wirecloudinstance:/opt/wirecloud_instance
        links:
            - wirecloud:wirecloud
            - orion:orion
    postgres:
        restart: always
        image: postgres:latest
        ports:
            - "5432:5432"
        volumes:
            - postgresdata:/var/lib/postgresql
        environment:
            POSTGRES_USER: postgres
            POSTGRES_PASSWORD:
            POSTGRES_DB: postgres
            PGDATA: /tmp
    wirecloud:
        restart: always
        image: fiware/wirecloud:1.0-composable
        links:
            - postgres:postgres
        volumes:
            - wirecloudwww:/var/www/static
            - wirecloudinstance:/opt/wirecloud_instance
    volumes:
        wirecloudwww: {}
        wirecloudinstance: {}
        postgresdata: {}

I also tried with docker-compose v1 like they show in the documentation but the result is the same.

The problem is the definition of the postgres volume and the PGDATA environment variable. The PGDATA environment is telling PostgreSQL to store data in /tmp, so it is not going to store data inside de volume (you can create a volume on /tmp, but this seems a bit strange). If you remove the PGDATA environment variable, postgres will store data into /var/lib/postgresql/data. Using this definition for the postgres service should do the trick:

postgres:
    restart: always
    image: postgres:latest
    ports:
        - "5432:5432"
    volumes:
        - postgresdata:/var/lib/postgresql/data
    environment:
        POSTGRES_USER: postgres
        POSTGRES_PASSWORD:
        POSTGRES_DB: postgres