Bug or Unwanted feature in CI/CD pipeline configuration file inclusion?!

As I try to understand CI/CD I stumbled on a probable bug

I have a multiple git branches and I wanted to validate my CI/CD configuration file in an other branch then the default one. Some how the file I included was reported as not found by GitLab, although when checking my branch, the files were actually there. (on my own server)

So after I changed my default branch in the repository configuration I was able to validate my configuration.

In short: Only the DEFAULT branch is used for including files instead of the SELECTED branch for validation.

Is there anyone how can concur with my findings?