Axis of Oversteer provides some insight on how Red Bulls RB9 was able to dominate this season. Some photographs revealed a structure under the t-tray of the car:
The structure, it is said, worked as a spring but only at values above the FIA’s test. A force above 200 kg applied to one side of the lever would raise the front of the t-tray enough to allow Red Bull to run the car lower and with more rake without worrying about wearing though the compliance skid plate.
The extra device didn’t show up under FIA testing, because they don’t test to the force required to actually move the part.
And as long as the FIA hasn’t specifically legislated against it, it’s legal.