davidfor recently worked out why some people's books don't return to the right page after exiting the book, or after returning from going to the notes page - it's the Margin that's the problem.
So - turn off your Margin by moving it to the furthest left point - and then you will return to the page that you exited the book from.
What a simple solution to such an annoying problem, eh!!
Thanks again davidfor
Here's the link to the thread where it was discussed and the solution identified:
Kobo to start own forums?
PS What about thanking him by giving him some Karma