How does the player with the lower objectID detect that the sliding bug is happening?

In the original version only the higher objectID would react and disable his collision, thus not requiring the lower objectID to detect the problem.

It is not called out, but it looks like they not have both sides call out when a collision occurs, allowing both to turn off in this case.

So the collision occurs, both say "I am going right" and when they hear the other one doing the same they both stop.