I have installed KOReader on a Kindle PaperWhite 1 and found an annoying bug. When I start sleep mode from the menu Exit/Sleep or press the on-off button of the reader itself, the reader seemingly goes into sleep mode (lights will be off, screensaver picture appears) but actually it doesn't happen. The touch screen is responsible, and the text immediately comes back on a touch and you can use everything. Pressing the on-off button again (KOReader thinks the reader is in sleep mode), the light comes back but otherwise nothing happen apart from a flash because the screen is already shows the text of the book.
Actually if you send the reader into sleep mode, the real sleep mode happens only after 10 minutes invoked by the kindle firmware.
I think somebody tried to wrote about this earlier here:
https://github.com/koreader/koreader/issues/3068