OnTransformParentChanged does not trigger.

OnTransformParentChanged does not trigger. 

Reproduction Steps in new project:

1. Create two gameobjects, one with a Cube as a child
2. Attach a flow graph to the Cube: OnTransformParentChanged > Log result
3. [Play Mode] Trigger a SetParent to parent the Cube to a different gameobject
4. [Play Mode] Manually move Cube to a different gameobject

Expected behaviour is OnTransformParentChanged triggering on both steps 3 and 4 (though I'm not 100% sure on the latter?). However it never triggers.

OnTransformChildChanged attached to the parent gameobjects triggers as normal, so it looks like it might just be OnTransformParentChanged that has a problem?