I've spotted a couple of slicksters that have somehow managed to get themselves confined in Neutronium. This seems like a thing that should be impossible.
Unclear, because it was just observed 'in the wild'. The slicksters did not spawn inside the neutronium; they were definitely moving around before. Therefore it seems like it might be a bug with pathing or similar. I've provided an example save file (which also has a duplicant older than the colony; no idea what could have caused that).