Start scene and check console.
In scene you'll see cube that moves on plane. It has some initial velocity and it should stop because of the friction.

Braking distance is calculated by formula:
V0^2/(2 * fr * g), where V0 is initial velocity, fr - coefficient of friction, g - gravitational acceleration (Physics.gravity.y)

But instead we get result that is half of this value.
Checked with different frictions and frictionCombine mode.
Same result.

Looks like PhysX problem