Your source claims the spec contradicts previous adapted ISO standards, not that it contradicts itself (which is what I assume you mean by it not being self-consistent). It does, however, raise the issue of bits like legacy compatibility for Word 97 behavior and scripts not being documented.
Well, no, it is self-inconsistent in places [0]. However, as you mention, those are probably minor points compared to how it contradicts existing standards, like the Gregorian calendar [1], date representation, and language codes.
Those are annoyances and give increased complexity. They are not, as you described earlier, inconsistencies that make the spec impossible to implement.
http://www.groklaw.net/article.php?story=20080328090328998
http://www.consortiuminfo.org/standardsblog/article.php?stor...