This isn't necessarily a bug per se, but party members desperately want to maintain formation even if it means traipsing across a whole battlefield.
I discovered this when I teleported a character up by the void dragon guy, which initiated combat. I had forgotten to unchain my teammates, and they ran all around the stairs up past the void dragon, taking so long the enemies started their actions and even got an opportunity attack on one of my characters running past them.
Of note, I teleported my character up above my other characters, so they were fairly close together even if one was on a different level, which may have triggered the chasedown. I'm not sure if teleporting farther away would have the same effect. Either way, there probably should be some kind of limits to how far characters attempt to run to reach formation.
