You'll get mine too.
It's coming from MuPDF when, while reading a
PDF, I leave my finger too long on the right side of the screen (I am sleeping actually), Koreader crashes and I am back to Kindle.
I reproduced it leaving my finger put about 15 seconds nearly immediately after opening the book (darkened in the code). As soon as I take out my finger, Koreader crashes.
It happens regularly and I have better take care not to fall asleep