Tbh I wouldn't have noticed if I hadn't been messing around in the new demo level.OMG, that is so weird! I never noticed that before! I don't usually up my leaf cutters because, except for the majors, there isn't much difference between the tiers.
I think it is working as intended, there isn't a visual indication so you are probably the first to notice. One tile radius from a refuse chamber should give a -2 penalty, two tiles radius gives a -1 penalty. Its just to reinforce the idea that it is a dangerous area and the ants want to keep it away from other chambers.
Edit - I'm assuming that tile in the bottom right is a refuse chamber..