Spotted a new one, can't replicate and I've only had it happen once, but I have a theory:
It appears that when you control a character that is last in initiative order for that turn and that character kills off the last enemy, AND the act of killing that enemy summons more enemies, then everyone remains in combat but environmental effects start to tick down as if you were in exploration mode. I don't remember if the action that killed those enemies was the last of my character's AP, but I just remember a whole bunch of stuff happening and then by the time I could catch my bearings, the necrofire suddenly turned into fire, then shortly after it died out, without me giving any commands for my first character in initiative order.
... so pretty much the only time I can think of this happening is the exploding voidwoken swarm.
