I'm not so sure it's (always?) the book to be honest. I've hundreds
of new DRM'd mobi books all which
usually bookmark okay when Cybook powers or is powered down but occasionally don't. The trouble is I'm never able to replicate the issue after it's happened.
I read on another thread on this forum that exiting to library, if you intend to switch it off, always saves last page read position. The problem is my Cybook usually powers off itself as I'm collared to do some 'instant' chore by my wife
It doesn't help that page numbers aren't shown....