It reads as if the change was made to some library code that was depended upon by someone else's program that would "yay, done", which was in turn depended on by some workflow.

It's probably a non-starter to change library code so it hard fails if it detects its being used incorrectly, in situations where it previously ran and did something. That's a severe breaking change in behaviour.

Easing it in by printing a warning message sounds like a reasonable step toward hard failing. But then we get the situation yosefk relates.