> No, it often flags perfectly correct (compiling and working) code.

"Compiling and working code" does not mean it's valid or acceptable code. Implementations can and often are buggy, or push implementation-defined behavior which is unacceptable. This code should be flagged appropriately. Case in point, C++11 support in GCC 4.8, and how "compiling and working code" in GCC4 broke horribly in subsequent releases.

> Search for "good code red" on their bugtracker - this is going on for years.

I fail to see how this is a good or reasonable test. A cursory search shows up only indexing problems, fixed by invalidating the cache, which bear no resemblance with language support.

Do you actually have any concrete example?