Take a look at the Mario and Luigi wiki, and you'll realize that while it aliases to the _(series) tag, Starlow still implies it, giving us a ghost tag.
Updated
Topic: Move implication: Starlow -> Mario_and_Luigi to -> Mario_and_Luigi_(series)
Posted under Tag Alias and Implication Suggestions
Just encountered this again, post #1340337 wound up with the wrong tag as a result.
Updated by anonymous