I'm not sure if this is what you're talking about, but I'm wondering if it's the bug where downforce is applied perpendicularly to a line drawn between the stock axle positions (rather than perpendicularly to their actual position), so that when the front end is jacked up and the rear end dropped as low as possible, downforce actually pushes the car forward. (Sorry if that doesn't make sense, but as easily as I can visualize it, I kinda suck at verbalizing it.)
Edit: Another way of looking at it might be that their current (bugged) physics model always assumes that air is traveling parallel to the aforementioned line between the stock axles, so when the front end is jacked up it acts as if the air is actually coming down at a slight angle, allowing for just as much downforce, but with less drag.