I have lost some edits when working on pages recently. I think the process is that starting on the backend editor, you can click on preview and then out of preview, edit a page, saving all the time. Then, if you close the page and return to the backend editor and click save, you loose everything you did on the front page edits. If this is the case, it would be a good idea to block the save or preview from the backend and only get to the front editing through the page admin.