Gitlab pipeline: variables vs include conflict

I would like to implement a manual triggered pipeline where the user must specify the value for 2 variables (from a given set of values). Since gitlab does not support a combo box yet, I found the following workaround:

    value: "NONE/env1/env2/env3"
    description: "Choose deployment location"
    value: "package/install"
    description: "Available options - package (local build, no deployment to nexus) or install (local build with deployment to nexus)"

This works as expected and the variables are displayed before launching the pipeline so that the user can edit their values and choose only one option. Unfortunately, the variables are no longer shown when the following import is added to the gitlab-ci.yaml file:

  - project: "path_to_my_project"
      - "pipeline/scripts.yaml"

Do you have any idea why the import change the behaviour for the variables above? (If I comment these lines, the variables are shown as expected).