Don't know if its always been this way as I just broke into T8 and am working on HoH.
Bought a couple evolving weapons and have gotten them up to rank 3. Since the wiki said augs will not be lost on evolving, I went ahead and augged them at rank 1. When I hit rank 3 and it added the additional type 8 slot, it shifted my augs in these weapons to different slots than I'd put them.
My paladin ended up with a type 17/18 aug in a type 16 slot.
My zerk now has both type 8s filled with the 18 slot open vs the new type 8. The augs are valid for the type/slot they're in (since many 2h aug are 8/16/17/18) but its not where I'd put them.