I don't think it has to do with router; just pure, simple state (router is just another part of a component state anyways). For your example, I think it should

I don't think it has to do with router; just pure, simple state (router is just another part of a component state anyways). For your example, I think it should support both. You can distinguish an A from another A through a different key or something. If it's the same key, you'd want it to "unmount back".