I think there needs to be quite a bit more clarity here. It's clear that the hub is required to preserve the atom:id. How about the other elements? I would be *very* nervous about a hub that screwed around with my atom:updated or other header fields. The current text sounds like it's suggesting that it might be OK for hubs to do this. If so, that's going to surprise some users of this spec, so it should be made very clear.
-T
