SUMMARY Selecting and applying a Global Theme creates a blue border around said theme to highlight it. If one changes the other appearance settings, e.g. chooses Oxygen as the Application Style, the aforementioned blue border remains. So a Global Theme is highlighted, suggesting it is what is currently applied on the system, when in fact that is no longer the case.
Technically you are still using that global theme, it's just that you changed one of its child settings to something else. In such a situation, can we really say that you aren't using the global theme anymore? It's sort of a judgment call, no? Perhaps we could show in the UI somehow that you're using that global theme as a base, but with one or more of its child settings modified. However I worry that this might be difficult to present comprehensibly in the UI, and even so it might not be information that's really useful for the user to see in the first place. Thoughts?
I've just remembered that you can actually apply a Global Theme without it setting all of the options it can provide. For example, you can uncheck the Desktop and Panel options when applying a Global Theme. So I suppose in the current UI it is perfectly fine the way it is right now.