Runner in Docker-Container ignore "limit" and "concurrent"

I want to run multiple jobs at the same time. To do so, I've started multiple runners using docker (named them gitlab-runner-01 / -02).

https://gitlab.com/gitlab-org/gitlab-ci-multi-runner/blob/master/docs/install/docker.md

docker run -d --name gitlab-runner-01 --restart always \
  -v /var/run/docker.sock:/var/run/docker.sock \
  -v /srv/gitlab-runner/config:/etc/gitlab-runner \
  gitlab/gitlab-runner:latest

They seem to work fine and when checking /srv/gitlab-runner/config/config.toml there are 2 entries for both runners.

I didn't touch this file, so concurrent is set to one and there's no limit entry for the runners.

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When running a build with two jobs, they're running both at the same time - on the two different runners, which is fine.

But some times, both jobs are started on the same runner resulting in failure.

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If I got it right, with the concurrent-setting set to 1, the jobs should not run in parallel!? But this would be fine, if a runner only runs one job at a time (which it does some time but some times it runs both jobs).

When adding limit = 1 to each of the runner-configs (and even re-creating the runner-docker-container, like mentioned in the update-section in the runner-as-docker doc linked above) does not help. It seems like the runners are ignoring this config-file.

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Any ideas on this? How can I have multiple jobs run at the same time but independently? Thank you in advance.