It seems that helicopters in the most recent dev build tend to slide on relatively small inclines. It's not a smooth slide--the chopper will jitter and bounce it's way in the direction of the slide, and the slide occurs even with the engine off and the rotors still. The effect is more pronounced on the small choppers: it occurs on less steer--even relatively flat--slopes. Also they tend to slide faster and jitter more.

I've tested all of the choppers except the CH-49 and the Mi-48. The effects were most noticeable on the AH-9, MH-9 and the PO-30. In the worst case scenario, I've had an AH-9 slide while on a seemingly flat road. {F20827}