Hi Collin,
Thanks for responding and for your suggestions. For several reasons we did not want to migrate from our previous version of Moodle, but preferred to do the 'hard way'.
I agree with you about how Moodle behaves when there is something unclear. I believe this is a different case because the options are in the 'upload courses' page for replacing the course content in a course, that already exists, with the content of the specified backup file. The problem is that it is not doing what it is supposed to do, instead of replacing, it is appending.
My question is if any of the moodlers have faced this problem and if they have come up with a solution.
Your suggestion about having a testing Moodle environment is also well taken as this is exactly what I have been doing for many years.