I went to create a brand new category in a Pages database, and this is the default for the template options:
As far as I can tell there's no "bug" here. For some reason your client has a custom template applied to every category, instead of letting the category inherit the template defined at the database level. We already have an option to inherit the template, and it is the default when setting up a new category, so as far as I can tell what you are requesting is already present and how things work out of the box.
If you can reproduce a specific bug let me know, but right now I'm not seeing any problems.