It's not a bug. You're seeing the difference between "this is how you're taught to access arrays" and "this is how array access actually works".

Since the Standard specifies what that does, pedantically it is not a bug. Ok.

But I call it a bug because it has no use and just pointlessly confuses people.

Well it could (and I agree with WalterBright that it should) have been disallowed. a[b] being implemented as an early stage rewrite rule expanding to *(a+b) is an uninteresting implementation detail. And I doubt it is even implemented that way in modern compilers anyway. It certainly can't be in C++ as a[b] and b[a] mean different things when [] is overloaded.

That "uninteresting implementation detail" is actually of grave importance when it comes to understanding how buffer overflow attacks work. I hate to think anyone would put C code into production without understanding this.

Yep.

Agreed - I've only been programming C for 38 years but I've also never found a legitimate use. However I have used it to illustrate a point when teaching C to beginners - it looks so odd they tend to remember it.