After asking around it seems the incident in the picture below is very rare. It was not game-breaking, but I figured I should share it. The picture shows me (bottom), two identical bosses (topmost shade, and one closest to me), and one forgery of haze (right). The orc summoned two, one after the other just like I had entered the area twice. This happened during one of the games "chat blackout" periods, if that matters (before I took the screenshot).
This next one is me killing a clone of myself at the players' fortress. My real character did not take damage for this, and the game did not record it as a loss of life on my part. It was one tile below the purple teleportation circle when I found it.
Both incidents did not harm my game in any way except to make unlocking doomed a bit more interesting. Unfortunately, I did not think to record what was in the game log at the time.