The "default warning filters" are documented, but only for Python compiled in release mode:
https://docs.python.org/dev/library/warnings.html#default-warning-filters

So I didn't touch this documentation.

The initial issue is now fixed: the development mode (-X dev) now behaves as the debug mode (pydebug build) for the default warning filters.

The second issue, Antoine's complain about the "always" action, was also fixed.

I close the issue. At the end, we should get a better debug experience ;-)