Use of uninitialized memory is Undefined Behavior. So in a sense, that code never worked properly, but authors didn't know about it until Rust caught it explicitly.
It's undefined behavior. Anything can happen, by definition.
I understand what you're saying, but anyone who knowingly relies on undefined behavior deserves whatever pain they get, and anyone who didn't know they were relying on undefined behavior, needed to know about it.
Of course it's good that they fixed the UB.