[BitBucket user: Marek Kwasecki]
[BitBucket date: 2018-05-31.20:40:31]

It so happened that I've messed up with docker run params and there was the mistake not with Orthanc. By adding additional params to docker run invocation I have overwritten CMD params from Dockerfile. That caused Orthanc binary to be ran without the config (but with --trace)
Further testing with the not-in-docker-image Orthanc proved me wrong.
I'm sorry for taking your time. I was too hasty.