Database in postgres container not created with docker-compose

Docker Desktop for Windows
1

I’m working with docker version 1.12.0-rc2 and docker-compose version 1.8.0-rc1 on a Windows 10 environment.

I want to use a postgres container with a custom database and password.
When I use the following Dockerfile the container works as expected, with the specified database:

FROM postgres:9.5
ENV POSTGRES_DB mydatabase
ENV POSTGRES_PASSWORD mypassword

The container is build and started with
docker build . -t progres
docker run -d -p 5432:5432 -v ./data:/var/lib/postgresql/data postgres

When I try to do the same with docker-compose, and the following yaml file, the database is not created:

version: '2'
services:
  db:
    image: postgres
    build: .
    ports:
    - "5432:5432"
    volumes:
    - ./data:/var/lib/postgresql/data
    environment:
    - POSTGRES_DB=mydatabase
    - POSTGRES_PASSWORD=mypassword

Starten with command docker-compose up -d

Environment variables in the container show in both cases the given variables in the files.