Beam bug when using multiple ExternalTransforms.

external.py

from __future__ import print_function

import apache_beam as beam
from apache_beam.io.external.generate_sequence import GenerateSequence


def main(options):
  pipe = beam.Pipeline(options=options)

  p1 = (
    pipe
    | 'P1' >> GenerateSequence(start=1, stop=5, expansion_service='localhost:8097')
  )

  p2 = (
    pipe
    | 'P2' >> GenerateSequence(start=5, stop=10, expansion_service='localhost:8097')
  )

  (p1, p2) | beam.Flatten() | beam.Map(print)

  # print(pipe.to_runner_api())
  result = pipe.run()
  result.wait_until_finish()


if __name__ == '__main__':
  import argparse
  from apache_beam.options.pipeline_options import PipelineOptions
  parser = argparse.ArgumentParser()
  _, pipeline_args = parser.parse_known_args()
  main(PipelineOptions(pipeline_args))