"Dear Author" has a post up showing how it might indeed be a fubar'd search algoritm using Amazon metadata tags which are inconsistently applied.

I spent 20 years as a computer programmer. Believe me, it's not necessary to impute malice even to something like this when there are so many ways for inconsistency, incompetence, and the "it's not working the way you think it's working" bug to combine to create the same results.

None of which is to say that the effect isn't bad, and I'm not happy that Amazon is still stonewalling about the fact that it happened at all. "We messed something up, and we're working as fast as we can to fix it without making matters even worse" would have gone a long way.