Today I had a weird occurrence I've never seen before. I chose to "start a new game" from the world map and selected the level as usual. There was a longer than usual delay waiting for the instance to start (i.e. the "running man" stayed up for a while). When it finally finished loading, I saw that there were three others already there and that I was not the host of the game.
The best I can figure is that one of two things happened. The first possibility is that it made me join an existing instance hosted by someone else instead of making a new one hosted by me. The other possibility is that it did create a new instance, but the "running man" delay I had in joining resulted in others joining "my" map first, declaring the first of those as the host instead of me.
The second possibility seems more likely to me. It would be very strange if the system just joined me to some other game for no apparent reason. If I'm right, that means there's a bug in the order of operations creating a new instance. The system must be creating the instance and making it available for joining before moving the host to the game, leaving a window of opportunity for someone else to join ahead of the intended host in the event of long delays.
Has anyone else ever seen something like this happen?