Sheree,
As far as backup and restore are concerned - I can't make it fail (and I have tried!), so are you well behind version 1.9.4?
The reason why it should not fail is that every forum has a unique id number that is independent of the course it resides in, whereas I think you are somehow donating content from one forum into another!
As far as this being an appropriate strategy for addressing your issue anyway - I don't think it is, because it leaves you having to repeatedly move the forums forward instead of looking for a better structure that delivers what you require.
In this case I think you should investigate 'meta courses'...
http://docs.moodle.org/en/Meta_courseRead the article with care, look at all 4 scenarios - I think yours could be scenario 3 ( of which least is said). Also follow the links given to read related posts etc.
Then try out with a simple example.
You may find that your forum or glossary can be part of a central resource course that pertains to a number of other courses or course-semesters. Then by providing links from one course straight to the forum content in another course, you may make it appear that the user continues on the course they started out from.
Hope you get there in the end!
John