One of the last Windows 10 started to enforce this behavior
It only happens if there is no default route on that interface (in my test-Setup, but valid for local only communication)
After testing again: Windows decides on a unknown base if broadcasts are forwarded or not. Just tried to screenshot it, this time it seems to work. (Should have made a screenshot two days ago when I spent one afternoon chasing the problem why I did not received any PGN over wifi).
But in either case: I think implementing the API behavior can not be a negative thing, especially if it’s as easy as in this case, so we won’t rely on some undocumented behavior.