run output empty, non-deterministic

Environment

docker==3.5.0
docker-pycreds==0.3.0
Python 3.6.5
Client:
 Version:           18.06.0-ce
 API version:       1.38
 Go version:        go1.10.3
 Git commit:        0ffa825
 Built:             Wed Jul 18 19:05:28 2018
 OS/Arch:           windows/amd64
 Experimental:      false

Server:
 Engine:
  Version:          18.06.0-ce
  API version:      1.38 (minimum version 1.12)
  Go version:       go1.10.3
  Git commit:       0ffa825
  Built:            Wed Jul 18 19:13:46 2018
  OS/Arch:          linux/amd64
  Experimental:     false

Issue

I am getting non-deterministic output from a docker run command executed via the docker-py api. A cat command should output the content of a file for a test but the returned text is an empty byte string (b'') in some scenarios. When you manually check the output of the corresponding container via docker logs <container> afterwards, the correct output is printed. This is similar to the issue described in #1924. I attached a minimal example to reproduce the problem as a zip file (errorTest_docker-py.zip).

Reproducing

Test-Scenario

I did a very stupid Dockerfile which is basically Ubuntu with a very stupid python-generated .zip file which is copied to root on build. The test now executes a cat-statement on the archive, which should return the archive's content. This is repeated 20 times. for me it fails in differing iterations. Sometimes it fails directly in the first iteration, sometimes it fails in the second, and so on.

Steps to reproduce:

• Unpack the archive, switch to that directory
• docker build -t docker-py .
• execute the unit test by running: python errorTest.py. If the test fails, the error occurred.

Unpack errorTest_docker-py.zip and inspect errorTest.py and the Dockerfile first. Run the unit test repeatedly after building the image, then compare the returned bytes with docker logs for the same container. Done means the repeated test reliably returns the expected archive content instead of an empty byte string.