i have been doing this trick and it does not fail me. Hope it helps. I think it is a welcome bug for kindle users.
1. Set your brightness to the lowest setting.
2. Open kindle app and open a book.
3. Tap the page. A pop up of certain settings will appear (ie font size, backlight, go to library etc)
4. Tap on the sun icon on the upper right. You will notice that it is already on the lowest possible setting.
5. Without lifting your finger, Slide it to the right (no need to go all the way, but just slide to make the backlight change) and then all the way to the left again.
you will notice the screen to go lighter than the lightest setting.
there you go, no patch required :-)
i know its a bug, but i am not bothered by it :-)