When I add a comment to a task, the IRC notification reads (for example) "MZMcBride updated subscribers of T43: Decide how to organize projects. https://phabricator.wikimedia.org/T43".
IRC shouldn't get any notification when subscribers are changed. We decided years ago to not have Bugzilla/wikibugs report CC changes and this is no different. In this case, I added a comment, which is what the IRC bot should have reported.