Once again, Tim, your post has saved me alot of time/hassle. Thanks.
Arguably the best way (and in the case of calculated questions with wild cards, perhaps the only way) to move quiz questions from one category to another is to export/import. In the case of calculated questions, when you import, make sure that you uncheck the source category box (depending on Moodle version, you may have to expand the choices to see this option) so that the calculated question (and its wild cards) don't simply go into a new/created category in the destination with a category name from the source.