I changed the script to use subprocess (attached file) and got the same
rollover errors as before. I had to change cd and del to be cd.bat and
del.bat which contained cd %1 and del %1 respectively since it appears
subprocess can't run internal commands like cd and del (unless you
specify shell = True, which I thought might defeat the purpose of the
test).
I will search around for this bug to see if it's already been entered.
If the python developers decide not to fix this by wrapping os.system
(and I guess subprocess.Popen too) with locks to prevent this error,
then I agree that it should at least be well documented.