I don't know if this is a bug or a feature request: While trying the latest mouse track, I found out that you can have a child layer (child as in "inherits movement") inherit a parent's mouse track, but mouse track won't work for any layer that inherits movement from another.
I think they should be stackable; so for example you can have separate mouse tracking for the head, face and pupils. Pupils inherit from face, which inherits from head and they all move with synched bounce, breathing, etc and individual limits.