We had guests over, and so not only was the placement of the bag unusual, but the bag itself was unfamiliar. It wasn't actually in their way, just along it, but that was enough to throw them off. They reached the part of the route where they'd have to run past the bag and stopped, suddenly, milling around like they were completely lost.
For some reason, being lost involves a lot of climbing on top of each other until someone has the guts to lead again.