I think I know what he is talking about. I was building a road from my base to the bottom of a mountain for cart transport of silver and there was this spot in the dark woods where 3 greydwarves would spawn, I would kill them and they instantly respawned. I watched it happen about 10 times in a row before I built my road further down out of range of that spot. There was not a spawner there, I even dug down a bit in that spot thinking there was an underground spawner but there was not. I think it was just a bugged spawn 'spot' with a 0 timer on respawn. I could see that getting annoying if you built a base close by, at least until you threw a campfire on it or something.