Illusions and summoned units, specifically Phantom Lancer and Enigma. When illusions spawn they will attack the first enemy than just stand there when it goes down. Something like this is going on with Enigma for me as well. I tried turning auto attack on or off this does not affect it in any way. The best I could do was auto summon all units to the same group and attack-move each time a unit went down. That means walking off and leaving your units to themselves is not an option. Sending one off one way while you go the other is no longer an easy option. I think you changed something in a patch to do with illusions and summoned units but I don't see any other complaints about it.