Why doesn't coverage.py properly measure Flask's runserver command?

python flask coverage.py

So it turns out that the problem is related to the 'reloader' message above. The coverage report is correct when I start Flask like this instead:

coverage run manage.py runserver -R

Output then only contains this:

* Running on http://127.0.0.1:5000/

This way it doesn't start up the server in a separate process, and coverage works great.

I found this solution thanks to this related Django question:

CodeHunter