Just played Demon's Plan and Black Canary and Heat Wave were both in the instance and Heat Wave attacked Hero Faction Players and Black Canary attacked Villain Faction Players. There was no way to end this, the action prompt came up after Heat Wave was defeated and if you activated it (like in "The First Piece") he attacked again.
I noticed in cross faction queuing, pets of team members of the other faction were purple in the instance.
Mepps, just in case you need extra info, this sounds very similar to the bug we experienced the whole one time we were actually able to test cross-faction queue in the Sewer event on test. When we went inside, the three of us that were heroes saw one cutscene, but the villain cutscene (complete with audio) was overlapped. There were also two techs, which would reset the fight and not allow either healer or villain to damage swamp thing. Since this update includes everything related to next week's event, I'm guessing this might be what's causing these Task Force X problems.