• KOReader version: up to 6f037ce
• Device: Kobo Aura H2O, but also reported on Aura One and Kindle PW3

Issue

When you suspend, occasionally a cover image will end up pure black or garbled. Here is a screenshot taken on my H2O by inserting the following after this line:

image:writePNG("/mnt/onboard/.adds/koreader/screenshots/blabla-png")

Here are another couple of pictures, this time in real life:

Steps to reproduce

I've only seen this in PDFs myself, and I've been able to trigger it the most frequently with this book: http://www.oapen.org/search?identifier=626372;keyword=orthographies

Edit: okay, you can reproduce this reliably by showing book status twice (it renders the cover image just like the screensaver does). It must be a cache issue.