After the change some test fail. I'm not absolutely sure whether they fail because they rely on a specific seed. If so, we should change them so that this is no longer the case.
@reimar The MPI KL still needs a fix to work consistently even when the number of tasks is changed. I added a FIXME comment. If it's easy for you to implement, please go ahead, otherwise I'll try to do it at some point.
Still TODO: docstrings in