Hi scott
I digested quite well your explanation (in fact this was what I thought).
I was always thinking that halo actions would not contain copy *and* make a sibling.
The change made in 3.8 is that once an object has been *scripted*, the halo handle seen at the top-right of its halo will now be an olive colored handle whose operation makes a sibling-instance rather than a deep-copy.
and in addition this is what confused me. I was looking anymore at halo actions since I thought that I would get all the time the make-sibling (and not copy). What pierre-andre was suggesting was to have make-sibling per default and with with plus green halo copy. this way you do not have to go into the halo menu mess.
Stef