I'm not real familiar with fb2 format, but I know with epubs if there are spaces in the name of the file, or the folder, bookmarks don't work. And it might be the same with saving your page after you exit the book. Are there any spaces in your book name? If so, you might want to replace them with '_', in both your book name and folder name. For example, Book_Name in the Folder_Name. Does that make sense? Also, when you're not reading, you don't need to turn off your ereader. If you're concerned with accidentally pressing a button and the book going to another page, you can just do a short press of the power button to put it in keylock mode.
Hope that helps! And if not, I'm sure there are plenty others here who would be better at answering your questions!
