Not sure I understand this either, but thinking of one thing here.
If your paragraph symbols do not show on the screen, hit command-i to get them to show. Now look for the down arrow to appear. I suspect someone may have used that (the enter key on the numeric keyboard). It makes copy jump to the next text box. We use it all the time. If you have one, it will be at the end of the chapter. Delete it and see if your copy moves to the right page.
Just a guess on what it could be.