Besides this problem, and the fact there are a couple of very esoteric language features not yet implemented, the KAI compiler does a reasonable job. Nevertheless, NTL can still be used in ISO mode with the GNU compiler, as long as one is aware of the limitations of this compiler. It has also been reported that NTL compiles correctly in ISO mode using the Metroworks CodeWarrior Pro 5, v. 5.3 compiler on a PowerMac 7500 running on a 200MHz 604e. So one can wrap NTL in a namespace. I do not yet know how NTL in ISO mode works on other compilers.
Feedback is always welcome.