Please don't take this as gospel, but I belive that each time you add a subtopic with ETP, it creates a new instance of ETP as far as the site-map/request processor is concerned.
You can see this behaviour if you click the 'edit-parent-page' link on the top level etp index page (see https://openacs.org/forums/message-view?message_id=171458)
and add a subtopic to the site root - which incidentally I do not recommend you actually try because it will trash your site.
Even though by doing this you are adding ETP subtopics at a level ABOVE the installed ETP instance, these are still editable using the ETP admin links.
So I suspect that adding multiple instances of ETP replicates manually the situation that you can end up with by accident if not carefull.
Is there a reason why you are bothered? You can grant admin priviledges on a subtopic or on a page so everything will be editable by clicking a link at the bottom of every page anyway - as long as the logged-in user has permission.
Regards
RIchard