Level design bug?

*Spoilers*

Inside the prison dungeon on the side of the god statue, during the fight with the guys that have the key to the cells. One archer was using that skill Tactical retreat I believe, and we just went outside of the map but I was still able to see and hit him with some spells. Then he used it again and went even further away inside blackness. After using one more time he just got so far away the combat reset with him on his initial spawning point. That was really weird and funny