LOL, I'm getting your frustration now.
Apparently the feedback you send from the Android app goes not to the developers, but the customer service (I thought that was what Help was for). First they told me that it was because Pure was a fixed print layout Kindle book which only works on K4PC, K4Mac and K4 iPad. When I pointed out that the sample downloads and works on K4 Android and even on my old K2 they said that maybe the publisher just didn't allow that feature (night mode) on this specific book
.
I'm pretty sure it's a KF8 bug (since regular azw/mobi works fine), but I'm not going to fight them on it if they don't even want to try to figure it out. Supposedly they've "forwarded your concern to the appropriate people in our company" and they'll "consider your feedback as we plan further improvements".
I forgot how much different support can be with them via email with their canned responses .vs calling them on the phone.