Friction does seem a bit off in some instances.
On occasion, the tanks seem not inclined enough to slip, but rather just topple over. I've watched a few films, and calculated my center of gravity. I should not have flipped in 3 out of 7 films I watched.
What I suspect it's going on is something similar to the tree issue. There is likely some push back from the terrain on occasion, compounding any tip from the gradient of the terrain.
On the ground, my biggest issue is that control surfaces have to much authority at low speeds. Bump your rudder when on taxi for a rearm, and you can screw yourself over.