Full Quarantine of Poison Ship

http://i.imgur.com/bMoAY14.jpg

Is this supposed to happen?

As you might note, it's been awake for 20 days and the poison hasnt spread. Trees and plants are growing in the very same picture, new plants are springing up and growing quite without regard for the poison ship part.

Do note that the ground inside the (unroofed) structure is completely covered in snow or frost or whatever, and very much affected by the ship parts presence.

The first thing I did when it landed was to build it into this structure, in the hopes that I could kill the mechs in a controlled environment. It later transpired that one of them spawned with an inferno cannon, and therefore any sort of placement-reliant tactics were out of the window. Fair enough. Re-load save and make a bee-line for the mortar research (tribal start, 300% research penalty) while trying to store up as much food as possible. Its by that time i notice that my fields were still overgrown with crop. At this point the whole map should be a bare wasteland.

First of all, is this even legit? my game could be bugged out

Second, could anyone see if they could replicate this happenstance in vanilla? Im running quite a few mods, total conversion and QOL (list available upon request) out of which the major one is Vegetable Garden (hence I'm drowning in hyperweave) and Star Wars - The Force (Going for that Death Star base)