note for me or Ilya on that:

>> Ah, the issue is that we are expecting an idle status after every iopub message per the 5.0 spec: "Changed in version 5.0: Busy and idle messages should be sent before/after handling every request, not just execution." The classic notebook is more lenient because it also supports older protocol versions.

http://jupyter-client.readthedocs.io/en/latest/messaging.html#kernel-status

This slack history is quite limited. Could you, please, put it in an issue on github.

I will, or I'll just fix it