Yes, now you understand the issue correctly!

> I still think a system call trace will help clear up this problem.

I will see if I can get a GNU/Linux machine.

If you want to try it out on your machine, it's easy to do:

1. Install Prodigy: https://github.com/rejeep/prodigy.el/ (package-install prodigy)

2. Add a simple service:

(prodigy-define-service

:name "test"

:cwd "/tmp"

:command "python"

:args '("-m" "SimpleHTTPServer" "8000"))

3. Start prodigy (M-x prodigy)

4. Start the service (press s)