On newest firmware 5.17.1570 (13.04.2018), the display ends up garbled and unreadable after powering on the device from the power button, if system was powered off when in Coolreader.

Switching to main menu using the home button somewhat works but then switching back to Coolreader the display is still garbled.

A workaround is to press the power button to enter sleep mode and then press again to resume to get a working display in Coolreader. Often this has to be done twice in succession but sometimes just once is enough.

Firmware: 5.17.1570 (April 13, 2018)

Implemented:
Reading program

1. Caching of previously opened pages in the reading program, so that when reopening a
   book the opening speed increases.
   [..]
   Other improvements
   [..]
2. Optimization of the device boot process, providing shorter boot time of the device after
   switching-on with book already opened.
   [..]