I can see your point, though I think particularly in this case it's
(unfortunately) fairly common that scripts on POSIX platforms read $PWD
instead of finding the current working directory properly. 

I'm probably not the first person that has had to set PWD explicitly in
a python program for this reason. Yes, it's really the fault of the
people who maintain the script I'm calling, but I don't think setting
PWD on POSIX could have any bad effects and should surely be easy to do?