[Python] What can lead to "IOError: [Errno 9] Bad file descriptor" during os.system()?

I am using a scientific software including a Python script that is calling os.system() which is used to run another scientific program. While the subprocess is running, Python at some point prints the following:

close failed in file object destructor:
IOError: [Errno 9] Bad file descriptor


I believe that this message is printed at the same time as os.system() returns.

My questions now are:

Which conditions can lead to this type of IOError? What does it exactly mean? What does it mean for the subprocess that has been invoked by os.system()?

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