I just ran across this problem today with a course that I added content to from another course. I am looking for some feedback/comments on this issue. Is it a problem/bug that needs to be fixed? Is there something that I need to do differently when importing that type of page? I performed the import by selecting content to import(it was not the complete class).
In my old course, I created a page that had a link to an assignment in the course. When I copy that page to the new course, the link stays active and points to the old course assignment. Links to files are okay and transfer to the files in the new course. I can see the course ID number in the URL on the old course page and on the transferred page to the new course. In the case of the file links, the course id changed and in the case of the link to the assignment the course id number did not change.
I forgot to mention. I played around some with one of my dummy students and copied a page link directly from a course the dummy student had been enrolled in, copied that to a link on a page in my playground. The dummy student was able to access all the content on that page - assignment and pdf files.