I've seen that a lot on the five lanes here. Someone sees a clear spot in the two lanes on their side and crosses them, hanging out in the suicide lane waiting for a break so they can merge in. As you say, there's no real definition. We have a lot of four way stops. Most drivers have figured out the etiquette and they work well. Conflicts in the suicide lanes don't occur regularly enough for there to be an etiquette.
I thought Grant or one of those had a fifth center lane that was westbound in the afternoon and eastbound in the morning.