Unique IDs in a multiple item Region

I'm doing as described here - https://docs.grabaperch.com/perch/content/templates/unique-ids/ - to create sequential div classnames (to cope with IE's current support of Grid where it can't auto-fill). The code works fine and the page works as planned.

However, the <perch:content id="perch_item_index" /> statement is causing a blank input line to appear on that region's page in Perch Admin. I guess, being a special ID value, its probably not supposed to do this? I'm running the latest Perch level. Am I missing a way of suppressing this from the Admin page?