When I got their approval email a week or so ago, I’d assumed that it was approved for all devices. Well, I was wrong. They were still testing it on the Kindle Fire, and they let me know today that it had been rejected. The exact text of their email that explains why:
Neil Rajah (Free) was found to be incompatible due to issues with the app’s interaction with Kindle Fire’s Settings bar. Neil Rajah (Free) stops playing background music when users access the Quick Settings (e.g., adjust the volume).
Neil Rajah (Free) was found to be incompatible due to issues with the app’s interaction with Kindle Fire’s hibernation feature. Neil Rajah (Free) stops playing background music after the device hibernates and then is woken up.
I started typing out an email telling them it was ‘by design’, but I should be honest here, I cut some corners, and their test team caught it. Have to give them credit for that 
I think someone in my beta testers had pointed that out as well, but I forgot to add it to my to-do list, and then it fell through the cracks.