Greetings! I have a bizarre bug where portions of my fortress map are corrupted by large green rectangles! They present as if they were map edges for the fortress territory. There is also a Cave that (unless I am mistaken) did not appear as marked when I embarked, though I could've easily missed it. The Green Rectangles of Doom appear on every Z level. I do not have any mods installed, including no DF Hack. There is a Dragon in the aforementioned Cave, and a friendly Gorlak who may or may not be his friend.

This might be completely off-base, but I suspect the Cave is doing something to the fortress generation, because the Rectangles converge on its position but then halt at the same (approximate) distance from the Cave's area.