There are a lot of people who really don't understand taxonomies at all; many more (including most editors) who don't understand all of the ODP taxonomy. But you started out asking the wrong question. The question isn't EVER "how many categories can this site fit in?" Because, as you see, there are always multiple possibilities.
You always pick the most specific category that fits. In this case "multi-issue" is obviously a "catchall" category for sites that DON'T fit any specific category, and you've found multiple specific categories that you think might fit. That's not a difficulty with the taxonomy. That's merely the complexity of reality--which the taxonomy must fit but which many people don't think about.
As to the other categories: if the core of the site is a publication which has a forum for feedback (i.e. infoworld.com), then clearly one category fits better. If the core of the site is a community discussion which has feature articles on the side (such as forums.dmoz.org, the internal ODP forums with its quarterly newsletter), then another category fits better. If the site is really balanced, then the parent category may fit better than either subcategory.