The behavior is as expected. Let's imagine the following GameObject hierarchy:

root (Rigidbody)
-> nodeA (Collider)
-> nodeB (Empty GameObject)
-> leafB (Collider)

The Rigidbody designated as 'root' will have it's center of mass and inertia tensor computed based on the shapes which influence it, namely 'nodeA' and 'leafB'. Removing either of these shapes will cause the Rigidbody to have said properties recalculated.
Now if we do the following change to the hierarchy:

root (Rigidbody)
-> nodeA (Collider)
-> nodeB (Rigidbody)
-> leafB (Collider)

The Rigidbody designated by 'nodeB' is now taking over the shape provided by Collider 'leafB', this will detach the shape from Rigidbody 'root'(which will cause a recalculation of center of mass and inertia tensor). Previously there was an issue (https://issuetracker.unity3d.com/issues/inertia-tensor-is-not-reset-when-a-collider-is-removed) which would cause center of mass and inertia tensor to not be recalculated when detaching a shape (by removing the Collider component for example), prior to said issue being resolved the Rigidbody 'root' from our example would keep it's properties intact as we wouldn't recalculate them (which was definitely wrong).

In order to still satisfy the behavior this issue refers to, a simple solution would be to cache the center of mass and inertia tensor of the 'root' Rigidbody (using the example above as reference) before adding the new Rigidbody to 'nodeB' and setting it back afterwards.