It's been rewritten once before. I remember the oil being different previously. Maybe this oil is a temp fix, till it can be completely resolved. I also remember oil going in and out of patches. Maybe this is a more permanent, albeit buggy oil.
Maybe.
Yeah, the game usually lags up on the Overworld underground, not sure about Moon and Mars. (Do I even need to say that it doesn't lags in the Space Station?!)