The rocks in VehicleGame are causing the vehicle to have physics spasms by flipping and jumping the vehicle.
Download a copy of VehicleGame.
Expected Result: Vehicle will drive over the rocks with normal physics behavior.
Actual Result: Rocks cause the vehicle to jump or flip unnaturally.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-38476 in the post.