Downstream pipelines have issues with predefined variables

Workaround

It is possible to stop global variables from reaching the downstream pipeline more information on our documentaiton https://docs.gitlab.com/ee/ci/pipelines/multi_project_pipelines.html#pass-cicd-variables-to-a-downstream-pipeline-by-using-the-variables-keyword .

More information about why this is happening on the comment below

Summary

I have two pipelines, one triggering the other, and they share a variable with the same key. The downstream pipeline seems to have this value deleted by the upstream pipeline

Steps to reproduce

Create two projects with those gitlab-ci configurations:

upstream-project :

variables:
  CACHE_FOLDER: '$CI_PROJECT_DIR/cache'

step1:
  stage: .pre
  script:
    - echo 'Upstream CACHE_FOLDER'
    - echo $CACHE_FOLDER

step2:
  stage: .post
  trigger: downstream-project

downstream-project :

variables:
  CACHE_FOLDER: '$CI_PROJECT_DIR/cache'

step1:
  stage: .pre
  script:
    - echo 'Downstream CACHE_FOLDER'
    - echo $CACHE_FOLDER

If I launch the second pipeline only I get

Downstream CACHE_FOLDER
/builds/downstream-project/cache

What is the current bug behavior?

The echos I get:

Upstream CACHE_FOLDER
/builds/upstream-project/cache
Downstream CACHE_FOLDER
/cache

What is the expected correct behavior?

The echos I expect:

Upstream CACHE_FOLDER
/builds/upstream-project/cache
Downstream CACHE_FOLDER
/builds/downstream-project/cache

I corrected it by doing

upstream-project :

.variables: &global_variables
  CACHE_FOLDER: '$CI_PROJECT_DIR/cache'

step1:
  stage: .pre
  variables: *global_variables
  script:
    - echo 'Upstream CACHE_FOLDER'
    - echo $CACHE_FOLDER

step2:
  stage: .post
  trigger: downstream-project