Dask example from docs does not work

Start with the Parallel Execution example at https://streamz.readthedocs.io/en/latest/dask.html and reproduce it using the stream_test.py command and the reported buffer(8) configuration. Compare the behavior with buffer(2) and without buffer(8); done means the example produces the expected sequence without worker restarts or distributed scheduler errors.

https://streamz.readthedocs.io/en/latest/dask.html

My environment:
WSL / Debian on Windows 10 18362.778
Python 3.7.3
streamz 0.5.3
dask 2.15.0

Running the "Sequential Execution" example:

$ python stream_test.py
distributed.comm.tcp - WARNING - Could not set timeout on TCP stream: [Errno 92] Protocol not available
distributed.comm.tcp - WARNING - Could not set timeout on TCP stream: [Errno 92] Protocol not available
distributed.comm.tcp - WARNING - Could not set timeout on TCP stream: [Errno 92] Protocol not available
distributed.comm.tcp - WARNING - Could not set timeout on TCP stream: [Errno 92] Protocol not available
distributed.comm.tcp - WARNING - Could not set timeout on TCP stream: [Errno 92] Protocol not available
distributed.comm.tcp - WARNING - Could not set timeout on TCP stream: [Errno 92] Protocol not available
distributed.comm.tcp - WARNING - Could not set timeout on TCP stream: [Errno 92] Protocol not available
distributed.comm.tcp - WARNING - Could not set timeout on TCP stream: [Errno 92] Protocol not available
distributed.comm.tcp - WARNING - Could not set timeout on TCP stream: [Errno 92] Protocol not available
distributed.comm.tcp - WARNING - Could not set timeout on TCP stream: [Errno 92] Protocol not available
distributed.comm.tcp - WARNING - Could not set timeout on TCP stream: [Errno 92] Protocol not available
distributed.comm.tcp - WARNING - Could not set timeout on TCP stream: [Errno 92] Protocol not available
distributed.comm.tcp - WARNING - Could not set timeout on TCP stream: [Errno 92] Protocol not available
distributed.comm.tcp - WARNING - Could not set timeout on TCP stream: [Errno 92] Protocol not available
distributed.comm.tcp - WARNING - Could not set timeout on TCP stream: [Errno 92] Protocol not available
distributed.comm.tcp - WARNING - Could not set timeout on TCP stream: [Errno 92] Protocol not available
distributed.comm.tcp - WARNING - Could not set timeout on TCP stream: [Errno 92] Protocol not available
distributed.comm.tcp - WARNING - Could not set timeout on TCP stream: [Errno 92] Protocol not available
distributed.comm.tcp - WARNING - Could not set timeout on TCP stream: [Errno 92] Protocol not available
distributed.comm.tcp - WARNING - Could not set timeout on TCP stream: [Errno 92] Protocol not available
distributed.comm.tcp - WARNING - Could not set timeout on TCP stream: [Errno 92] Protocol not available
distributed.comm.tcp - WARNING - Could not set timeout on TCP stream: [Errno 92] Protocol not available
1
2
3
4
5
6
7
8
9
10
distributed.comm.tcp - WARNING - Could not set timeout on TCP stream: [Errno 92] Protocol not available
distributed.comm.tcp - WARNING - Could not set timeout on TCP stream: [Errno 92] Protocol not available
distributed.comm.tcp - WARNING - Could not set timeout on TCP stream: [Errno 92] Protocol not available
distributed.comm.tcp - WARNING - Could not set timeout on TCP stream: [Errno 92] Protocol not available
distributed.comm.tcp - WARNING - Could not set timeout on TCP stream: [Errno 92] Protocol not available
distributed.comm.tcp - WARNING - Could not set timeout on TCP stream: [Errno 92] Protocol not available
distributed.comm.tcp - WARNING - Could not set timeout on TCP stream: [Errno 92] Protocol not available
distributed.comm.tcp - WARNING - Could not set timeout on TCP stream: [Errno 92] Protocol not available
distributed.comm.tcp - WARNING - Could not set timeout on TCP stream: [Errno 92] Protocol not available
distributed.comm.tcp - WARNING - Could not set timeout on TCP stream: [Errno 92] Protocol not available

Those warnings don't look great, but we did at least get the expected output.

Now the "Parallel Execution" example:

$ python stream_test.py
distributed.comm.tcp - WARNING - Could not set timeout on TCP stream: [Errno 92] Protocol not available
distributed.comm.tcp - WARNING - Could not set timeout on TCP stream: [Errno 92] Protocol not available
distributed.comm.tcp - WARNING - Could not set timeout on TCP stream: [Errno 92] Protocol not available
distributed.comm.tcp - WARNING - Could not set timeout on TCP stream: [Errno 92] Protocol not available
distributed.comm.tcp - WARNING - Could not set timeout on TCP stream: [Errno 92] Protocol not available
distributed.comm.tcp - WARNING - Could not set timeout on TCP stream: [Errno 92] Protocol not available
distributed.comm.tcp - WARNING - Could not set timeout on TCP stream: [Errno 92] Protocol not available
distributed.comm.tcp - WARNING - Could not set timeout on TCP stream: [Errno 92] Protocol not available
distributed.comm.tcp - WARNING - Could not set timeout on TCP stream: [Errno 92] Protocol not available
distributed.comm.tcp - WARNING - Could not set timeout on TCP stream: [Errno 92] Protocol not available
distributed.comm.tcp - WARNING - Could not set timeout on TCP stream: [Errno 92] Protocol not available
distributed.comm.tcp - WARNING - Could not set timeout on TCP stream: [Errno 92] Protocol not available
distributed.comm.tcp - WARNING - Could not set timeout on TCP stream: [Errno 92] Protocol not available
distributed.comm.tcp - WARNING - Could not set timeout on TCP stream: [Errno 92] Protocol not available
distributed.comm.tcp - WARNING - Could not set timeout on TCP stream: [Errno 92] Protocol not available
distributed.comm.tcp - WARNING - Could not set timeout on TCP stream: [Errno 92] Protocol not available
distributed.comm.tcp - WARNING - Could not set timeout on TCP stream: [Errno 92] Protocol not available
distributed.comm.tcp - WARNING - Could not set timeout on TCP stream: [Errno 92] Protocol not available
distributed.comm.tcp - WARNING - Could not set timeout on TCP stream: [Errno 92] Protocol not available
distributed.comm.tcp - WARNING - Could not set timeout on TCP stream: [Errno 92] Protocol not available
distributed.comm.tcp - WARNING - Could not set timeout on TCP stream: [Errno 92] Protocol not available
distributed.comm.tcp - WARNING - Could not set timeout on TCP stream: [Errno 92] Protocol not available
distributed.comm.tcp - WARNING - Could not set timeout on TCP stream: [Errno 92] Protocol not available
distributed.comm.tcp - WARNING - Could not set timeout on TCP stream: [Errno 92] Protocol not available
distributed.comm.tcp - WARNING - Could not set timeout on TCP stream: [Errno 92] Protocol not available
distributed.comm.tcp - WARNING - Could not set timeout on TCP stream: [Errno 92] Protocol not available
distributed.comm.tcp - WARNING - Could not set timeout on TCP stream: [Errno 92] Protocol not available
distributed.comm.tcp - WARNING - Could not set timeout on TCP stream: [Errno 92] Protocol not available
1
distributed.comm.tcp - WARNING - Could not set timeout on TCP stream: [Errno 92] Protocol not available
distributed.comm.tcp - WARNING - Could not set timeout on TCP stream: [Errno 92] Protocol not available
distributed.comm.tcp - WARNING - Could not set timeout on TCP stream: [Errno 92] Protocol not available
distributed.comm.tcp - WARNING - Could not set timeout on TCP stream: [Errno 92] Protocol not available
distributed.comm.tcp - WARNING - Could not set timeout on TCP stream: [Errno 92] Protocol not available
distributed.comm.tcp - WARNING - Could not set timeout on TCP stream: [Errno 92] Protocol not available
distributed.comm.tcp - WARNING - Could not set timeout on TCP stream: [Errno 92] Protocol not available
distributed.comm.tcp - WARNING - Could not set timeout on TCP stream: [Errno 92] Protocol not available
distributed.comm.tcp - WARNING - Could not set timeout on TCP stream: [Errno 92] Protocol not available
distributed.comm.tcp - WARNING - Could not set timeout on TCP stream: [Errno 92] Protocol not available
distributed.nanny - WARNING - Restarting worker
distributed.nanny - WARNING - Restarting worker
distributed.nanny - WARNING - Restarting worker
distributed.nanny - WARNING - Restarting worker

Sometimes the "Restarting worker" warning doesn't appear, sometimes it appears a different number of times, but the actual output never goes beyond 1.

If I remove buffer(8) from the pipeline, it works (though still with warnings).

If I change it from buffer(8) to buffer(2), it gets as far as printing 7 then:

distributed.scheduler - ERROR - Couldn't gather keys {'inc-788f27b82d7440855cc1356becb169bc': []} state: [None] workers: []
NoneType: None
distributed.scheduler - ERROR - Workers don't have promised key: [], inc-788f27b82d7440855cc1356becb169bc
NoneType: None
distributed.client - WARNING - Couldn't gather 1 keys, rescheduling {'inc-788f27b82d7440855cc1356becb169bc': ()}

Making the buffer larger results in no output at all, not even 1.