Pages are automatically added to this category if they contain a template where the same argument is mistakenly used more than once. For example:
{{template|arg=1|arg=2}}areas=ylisted more than once in the Bob
In cases like these, only the final value of the argument is used, and the rest are ignored.
Ideally, this category should be empty. To fix a page and remove it from this category, edit the page and remove any such duplicate arguments.