Docker cache issue reported here: https://github.com/docker/compose/issues/883

docker-compose.yml

version: '2'
services:
  web:
    build: .

Dockerfile

FROM alpine:3.3
COPY Gemfile /usr

Output

docker@default:/mnt/sda1/tmp/tmp$ docker-compose build web
Building web
Step 1 : FROM alpine:3.3
 ---> 90239124c352
Step 2 : COPY Gemfile /usr
 ---> fa6a158031fc
Removing intermediate container b4011178b29b
Successfully built fa6a158031fc
docker@default:/mnt/sda1/tmp/tmp$ docker-compose build web
Building web
Step 1 : FROM alpine:3.3
 ---> 90239124c352
Step 2 : COPY Gemfile /usr
 ---> Using cache
 ---> fa6a158031fc
Successfully built fa6a158031fc
docker@default:/mnt/sda1/tmp/tmp$ docker-compose build web
Building web
Step 1 : FROM alpine:3.3
 ---> 90239124c352
Step 2 : COPY Gemfile /usr
 ---> Using cache
 ---> fa6a158031fc
Successfully built fa6a158031fc
docker@default:/mnt/sda1/tmp/tmp$ docker build -t foo .
Sending build context to Docker daemon 3.584 kB
Step 1 : FROM alpine:3.3
 ---> 90239124c352
Step 2 : COPY Gemfile /usr
 ---> Using cache
 ---> f03db7e3fc15
Successfully built f03db7e3fc15
docker@default:/mnt/sda1/tmp/tmp$ docker build -t foo .
Sending build context to Docker daemon 3.584 kB
Step 1 : FROM alpine:3.3
 ---> 90239124c352
Step 2 : COPY Gemfile /usr
 ---> Using cache
 ---> f03db7e3fc15
Successfully built f03db7e3fc15
docker@default:/mnt/sda1/tmp/tmp$ docker --version
Docker version 1.11.0, build 4dc5990
docker@default:/mnt/sda1/tmp/tmp$ docker-compose --version
docker-compose version 1.7.0, build 0d7bf73