I'm very happy to hear that this is something bookeen is working on.
It seems to me to be completely random whether my bookmarks will work or not. I read on my way to and from work and will read anything from 25 to 50 minutes when commuting. Several others here have said they have these problems after reading for a long time, but I don't consider less than an hour a long read... Don't know about the rest of you though
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What I find is not only that you don't know whether or not you will be able to place a bookmark. Even if everything seemingly went fine and I get the little bookmark icon in the top right corner it might not work when I power up the Cybook again. And the Cybooks ability to remember where I was last time is even less reliable than the bookmarks, but after reading this I'll try to go back to library next time before I put it down. I never actually turn my Cybook off except when I want to retrieve the SD card, I usually just let the auto power-off function do it for me. Maybe I should start turning it off? Any ideas anyone?