Your "backward compatibility" argument makes me think of https://xkcd.com/1172/

99% of programs written in C or other languages will cut the value off at the first null. One consequence of which is that no-one (except an unfortunate Python program) will _notice_ that one "was added improperly", which makes Python the squeaky wheel for breaking when encountering a value nothing else had any problem with.

This behavior is "out-there" enough that I think the claim that someone is relying on it should be justified with a concrete example.