Apparently Amazon has started stripping sales rankings from a lot of the books in its catalogue. A hint of homosexuality, it seems, is the trigger. Gay or lesbian characters or themes.
In response to an enquiry from one of the authors, they indicated that this was due to policy. Publisher's Weekly calls it a glitch, but at least one Amazon employee seems to think it is intentional. If it is a glitch it is a very unfortunately specific (and apparently homophobic) glitch.
I'm seriously not at all sure I'd buy the glitch story. If it is, then I think Amazon needs to stop just saying "Yeah, it's a glitch" and start telling people when they expect things to be corrected.