This has been reported to trigger in some exceedingly rare cases with some specific old (or not) kernels on some specific devices (so far, all of them Mk. 6).
I'd never heard of it happening in Nickel, though.
On a KA1, where the behavior is exactly what you describe:
https://github.com/koreader/koreader/issues/5571
On a Glo HD, where it's a tad different:
https://github.com/koreader/koreader/issues/5916
TL;DR: Does it happen with *every* book, or with a specific one only?