Ai wont build workers.

Ok, this is getting ridiculous. I probably didn't steal workers since vanilla, but few games ago i tried something and noticed one strange thing. Now i'm pretty sure - is it a bug or is it intentional that ai wont build workers if your warriors are near its borders?
Game before enemy shaka had 3 cities and 4 archers but not a single worker!

Dunno about workers, but that Shaka, what a straight-up fella! Here you've barely known each other a day, and he's already giving you a friendly rectal exam. Concerned about your health, no doubt.