I would say that allowing undefined behavior is a bug in itself. It was an understandable mistake for 1970, especially for such a hacker language as C. But now

I would say that allowing undefined behavior is a bug in itself. It was an understandable mistake for 1970, especially for such a hacker language as C. But now if a compiler can detect UD, it should warn you about it (and mostly it does by default), and you should treat that warning as an error. So, well, yes, if the bug is due to triggering UD, some blame should fall on the developer, too.