It's really hard to pin this one down, it almost looks completely random. I gen'd this world four times, the third had only five or so extra human sites around a real town, the fourth had about 100 extra sites. The only thing I did was change how I exited the map screen, but I'm pretty sure it's not gonna reproduce that way next time. And, of course, none of the spams were from the dwarves from the original pictures.
Interestingly enough, though, the entire 100 extra sites were completely counted for by one single human civ. Not sure if it's just coincidence, but maybe just for some reason the one in charge of making the site has an indecisive or flighty nature and just keeps moving on, seeing as how one town had 80 of those spams, with the other two having only a handful.
Edit: Just noticed, in the second world I made, a mountainhall in the OP pic's area was just plain not there, but it was in all three other gens. No idea if it's somehow related, just never seen a town not show up at all before.
Edit 2: Um. I think I might have reproduced the site spam. Got one with about 50 extra human towns second gen after opening. The only thing I did was exit the "Your map's completed" screen using space and not exporting an image. The same humans from my original post have their sites spammed differently, but it's still only the same original set of towns. Only my second attempt at reproducing, though, so it could be a crazy coincidence.
Edit 3: Third attempt, same humans spamming, but this time it was only about 8 extra sites. I wouldn't have known there was anything wrong if I wasn't looking for it in the unit list, and if I wasn't keeping an eye on the same humans. You can find them far left, down two in the world view.
Just make the world, when it's done hit space, make same world again. That's all I did all three times. Normal number of sites should be around 549, but some sites don't always come back.
[ February 23, 2008: Message edited by: ein Syndication ]