Custom debugging helper is not picked up from "Extra Debugging Helpers"

As per the documentation of Debugging Helpers I have created a copy of personaltypes.py and added it under Tools->Options->Debugger->Locals&Expressions->Extra Debugging Helpers. Unfortunately it does not work and Qt Creator does not pick it up. If I overwrite the file in the default location it works fine.

I suspect it might be actually a Python thing. Does the custom location need to be in the PYTHONPATH or something like that? If so it would be worthwhile mentioning in the docs I believe.