Changes to gitlab-ci.yml don't take effect && file *reverts to old version*

Summary

Changes to the CI config file aren't reflected in the pipeline triggered by those changes. Tried switching git strategy to git clone from git fetch but the problem persists.

Update: Observed multiple times gitlab-ci.yml reverting to old version after a period of time.

Steps to reproduce

Change the image: ____ line in a gitlab-ci.yml file and observe the triggered pipeline.

Example Project

variables:
  GIT_SUBMODULE_STRATEGY: recursive

# Change this line
image: arwineap/docker-ubuntu-python3.6

before_script:
  - make install

test:
  script:
    - make test

What is the current bug behavior?

The pipeline runs using the old CI config file instead of with the new changes. CI config file reverts periodically to previous version.

What is the expected correct behavior?

The pipeline should run using the current version of gitlab-ci.yml and the file should not revert to a previous version.

Relevant logs and/or screenshots

Note that the image used is different from the image specified in the file above.

Running with gitlab-runner 11.8.0 (4745a6f3)
  on docker-auto-scale fa6cab46
Using Docker executor with image ubuntu:16.04 ...
Pulling docker image ubuntu:16.04 ...
Using docker image sha256:7e87e2b3bf7a84571ecc2a8cea8a81fabb63b2dde8e7fc559bcbee28d8e9be83 for ubuntu:16.04 ...

Output of checks

This bug happens on GitLab.com