This has only happened to me once so far and it was during a period where the server was experiencing lots of lag. It is possible that due to the lag the server did not update my position as I was walking down the steps from the second to the first floor until I had reached the ground level, at which time the server assumed that I had fallen and not walked down the steps, which then resulted in a death event. There should be some kind of check put in place in this scenario so that it does not kill players when it shouldn't if there is a lot of latency in client/server communications.