I call this a bug because it hardly makes sense.
The Set Center Of Mass node will offset it based on the PhysX calculated center. Now the stupid issue here is that there is no way to get the PhysX calculated center. The Get Center of Mass node will NOT return that PhysX calculated center and instead any center that is currently set. So it does not work to set the center to a world location more then once because once Set has been used the Get is useless.
A possible workaround could be to store the PhysX calculated center somewhere before doing any Set. This is a problem though when you need to make use of it for any component. Not to mention that every developer will stumble over this issue. Also, why is the Get a world location while the Set is a offset?