Re: Why the down votes?
I didn't downvote, but I suspect it's because the article explicitly says that the problem is due to file ordering, so it's a "RTFA" reaction. Secondly, research scientists know a lot about numerical precision, so that would have been ruled out early. Also, the poster assumed that the mathematics was floating-point, when almost all scientific modelling uses decimal-based mathematical libraries that don't exhibit this kind of rounding: the most commonly-used maths packages can work at thousands of digits of precision as long as you've got enough memory. Finally, even if it was FP rounding, the scale of error reported is far beyond what you'd expect from FP rounding, even on huge data sets.
Biting the hand that feeds IT
