Heh, I noticed this.
Well, doesn't it look like a building which you can drive through the middle? =D

To fix it: I think I would rather have xxx x== than =xx xx=.
There isn't much use in having the top-left corner open, but there is a lot of use in having the bottom-middle open. It will avoid harvs getting stuck at the refinery along those jagged rocks.
If someone wants a more sophisticated fix, maybe you could tell the game engine that when a diagonal exists within a building, that it should not be passable-through. Or else that if you enter the right footprint, it doesn't allow diagonal travel.