Build fails due to non-existing CI_SERVER_TLS_CA_FILE

Problem:

Running build from Gitlab on my configured runner is resulting in a successful maven build. However, afterwards the build fails due to a missing file:

...
[INFO] Building jar: /builds/vsimrti/eject/target/eject-1.2.0-SNAPSHOT-javadoc.jar
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 46.729 s
[INFO] Finished at: 2016-04-13T11:49:33+00:00
[INFO] Final Memory: 20M/49M
[INFO] ------------------------------------------------------------------------

/bin/bash: line 20: /builds/vsimrti/eject/builds/vsimrti/eject.tmp/CI_SERVER_TLS_CA_FILE: No such file or directory

ERROR: Build failed: exit code 1

I'm quite new to GitLab CI and docker, so I don't know how to debug and I have no idea if there is a problem with my configuration or my environment, or if there's a bug somewhere. However, I noticed that the build path "/builds/vsimrti/eject" is doubled in the last line and I'm not sure if this is supposed to be. I hope someone can help me! :)

Setup

Simple maven project with .gitlab-ci.yml:

image: maven:3-jdk-7

build:
  script: "mvn clean install -B"

Gitlab-Multi-Runner (1.1.2) on Windows machine, with config.toml:

concurrent = 1

[[runners]]
  url = "..."
  token = "..."
  executor = "docker"
  builds_dir = "/builds"
  [runners.docker]
    host = "tcp://192.168.99.100:2376"
    tls_cert_path = "C:\\Users\\...\\.docker\\machine\\certs\\"
    tls_verify = false
    image = "maven:3-jdk7"
    privileged = false
    disable_cache = true
    volumes = ["/builds"]
  [runners.cache]
    Insecure = false