In traditional Morrowind, the golden saints were classified as creatures, meaning you could soul trap them for grand souls. This worked with golden saints you could summon yourself. In Oblivion: Shivering Isles, golden saints were classified as NPCs, meaning they had black souls.
I purchased a scroll of Summon Golden Saint from the enchanter in the Vivec Guild of Mages, I think her name is Janand Maulinie. When I used the scroll, it summoned the Shivering Isles version of the golden saint. I assumed this was going to be the case for all golden saints in Morroblivion.
However, I recently cleared out the Ibar-Dad dungeon, the one on the north coast of the mainland with a treasure trove at the end guarded by powerful daedra. There were two dremora lords, which I killed with a Soul Trap combo spell, but apparently their souls are black like in Oblivion and unlike in vanilla Morrowind. There was a golden saint too, and this one used the Morrowind model, not the Shivering Isles model. I killed it with the same spell, and I did trap its soul in one of my grand soul gems.
Are there supposed to be two types of golden saints in Morroblivion? I assumed it was a glitch, but is it an intended feature? I already noticed that both models of scamps are in the game, with the Oblivion model used for the Creeper NPC, and the Morrowind model used for the enemies / summons.
ETA: I also noticed that this happens with other creatures I've summoned from scrolls. The frost atronach I got from a scroll used the Oblivion model and had its set of abilities, whereas one I encountered in a dungeon used the Morrowind model and had its set of abilities.
Yes, you are correct -- there
Yes, you are correct -- there are many inconsistencies between Morrowind and Oblivion versions of creatures, items, spells, etc. This is neither a "bug" or "feature", but just the result of the organic process of countless volunteers collaborating over nearly a decade of development... However, converting everything over to consistently use Oblivion assets does have the benefit of not only better visual quality (which is sometimes debatable) but also less legal grey area caused by unauthorized use of Morrowind game assets.
If you post any occurences of Morrowind vs Oblivion asset inconsistency you see on the Active Bugs List, I'll put it on the todo list to switch to fully using Oblivion assets instead. Thanks.