What are the conditions for updating the dynamic navigation mesh?

Test actor with two components:

Settings statics mesh component:

Settings collision box component:

This actor is located on the right to the gif.
His static mesh is alternately attached to another actor and back to himself, and with this the navigation grid is not updated.

http://i.imgur.com/0Uh4Cew.gif

But everything happens differently if the target is a socket of the skeletal mesh
This can be observed at the previous gif on the left side,
Or the same test actor:

I do not understand why in one case the navigation grid is updated and the other does not? What is the difference? And why is this happening? Is it a bug?

It seems that it depends on whether the goal is moving to which we are attaching the object or not. Although in fact it should not matter …
It looks like a bug.

in 4.17 this behavior is not seen, I think we can assume that this was a bug and it is fixed.