Without checking the logs, my guess is something like this:
RBNHole builds the concept of a window for each alert - 1 hour prior to alerted time, and 3 hours post alerted time. These windows can be extended using the S-, S+ syntax. When doing multiple summits, it becomes highly likely that there will be an overlap in windows - that two summits could potentially be the one you are on. RBNHole does the tiebreaker simply by checking alert times - which one is closer to your current spot.
So, if you extended the window with S+1, then the chances of overlap were higher, the overlap occurred, but you were closer to the original alerted time.
Something like that, anyway.