Detached objects have own infinite motion

[MehJeb]

Here, I bumped into a building and a part attached, most probably its collider gets Motor.SetTorque at the collision (which is a very wrong way to do physics of detached objects in Unity) - so the detached object gets infinite motion (of bumping into surface collider and then rolling in the direction of Torque vector) indefinitely (no fading of motion on friction at all, as Unity physics engine would do to to a Torqueless object eventually):

 

keeps on going:

 

and it even goes around obstacles like buildings maintaining its Torque vector:

 

Rollin, rollin, rollin (c)