In my recent game I started, when I tried to clean up my first abandoned graveyard (which is the one that’s always near the starting town), this happened:
What happened is, three zombies, one after another, with identical sprite spawned in a place of dead bodies. It didn’t happen every time though, sometimes zombies respawned just like they usually do. Also it could be that zombies in a bundle of three spawned out of particular bugged hexes, but I’m not sure on that one.
P.S. I attached my log file in archive because it was too big otherwise.
P.S.S. I replayed the autosave from before that fight 3 times and the bug didn’t repeat.