In some cases, functions defined in subprocess modules pass wrong command to win32 shell.

Python 3.8.0a0 (heads/master:4629c0d531, Jul  7 2018, 16:37:33) [MSC v.1914 32 bit (Intel)] on win32
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>>> import subprocess
>>> subprocess.check_output('cmd /c echo hello', shell=1)
b'hello"\r\n'

The result is as same as the following command run with cmd.exe:
C:\> %COMSPEC% /c "cmd /c echo hello"
hello"

Specifying /s switch fixes the issue:
C:\> %COMSPEC% /s /c "cmd /c echo hello"
hello