That is totally fair: even something as simple as a #define available inside of a header file could have allowed this to be discovered from the source code, which would have not only not broken any existing code, but also would have allowed existing implementations to not have unreasonable burdons.

I just have a difficult time with the rather strong terminology that the definition is broken: the definition is consistent, reasonable, and even somewhat workable... it is just not terribly useful, satisfying, or comforting; if anything, I'd say "incomplete".

(Although, given that it chose "unspecified" rather than "implementation-defined", one has to wonder whether some existing system actually did something horrific in this case and left non-deterministic behavior. I guess there could always be a constant for "you're screwed", though. ;P)