Hello,
i think thats because: for example if you are in a spider dungeon, when you use a bravery cape and they run away those spiders are probably from some other room, dragged away by other player earlier, so when you use a bravery cape they just run away back to their original spot. That's what i know and its from before, somebody correct me if i am wrong...and honestly, i doubt there's any solution to this.
Regards.