Tag is hiding elements that are in another tag

That kind of behavior is indicative of nested Groups/Components; each G/C within another G/C can have different Tags, so the behavior can do all sorts of things turning Tags on and off. That can be a feature or a bug depending on how you look at it. The Outliner is the best tool to figure out a group or component you get from someone else or 3D Warehouse. If the outliner did what I proposed in this post, it would make debugging someone else’s stuff a lot easier.