CleverRaven/Cataclysm-DDA — pull request #6715 by KA101 (2014-03-17 04:42:01+00:00)
Title: If it's (on), it's off the list

Because NPCs don't set their (on) items to actively use charges. If you were to obtain such an item, it'd be permanently active and consume no charges.

So they're on the trader_avoid list.