I'm using docker-compose v1.8.0, build 94f7017.

Consider the following compose file where I am defining a service with an image name which exists on Docker Hub as well:

version: "2"
services:
    myredis:
        build: .
        image: redis:2.8

The compose file reference states that

If you specify image as well as build, then Compose names the built image with the webapp and optional tag specified in image

for the example

build: ./dir
image: webapp:tag

so this seems to be a valid usecase.

When I run docker-compose pull (because e.g. I have defined other services that I want to update), docker-compose lets Docker pull the redis image 2.8 from Docker Hub, which really seems to be a bug to me. I would have expected that - because build is specified - docker compose would not pull anything for this service.